Abstract:
In a nut disengagement prevention structure, a bolt has an external thread. A nut which is thread on the bolt has an internal thread. A thread portion which is the closest to a leading end of the bolt has a first minor diameter. Any other portion of the thread of the bolt has a second minor diameter which is smaller than the first minor diameter. The second minor diameter is substantially identical with a minor diameter of the internal thread of the nut.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a nut disengagement prevention structure, and more particularly to a nut disengagement prevention structure of the type in which a nut, once threaded onto a bolt, is held against withdrawal unless an artificial external force is exerted on the nut. 
     For example, for connecting a battery cord  3  to an electrode  2  of a battery  1  mounted on an automobile, an annular connection portion  4   a  of a battery terminal  4 , press-fastened to a distal end of the battery cord  3 , is fitted on the electrode  2 , and then a bolt  5  is passed through passage holes  4   c , formed respectively through a pair of clamping piece portions  4   b  and  4   b , and is tightened to be fastened, together with a washer  6 , to a nut  7 . As a result, the annular connection portion  4   a  is deformed to be reduced in diameter through the pair of clamping piece portions  4   b  and  4   b , so that the battery terminal  4  is fixedly secured to the electrode  2 . 
     For effecting the above operation in the vehicle-assembling process, the bolt  5 , passed through the passage holes  4   c , is beforehand loosely tightened relative to the nut  7 . Namely, the battery terminal  4 , having the bolt  5  and the nut  7  beforehand connected thereto in an integrated manner, is fed to a production line where the nut and the bolt are finally completely fastened together. 
     In such form of use, however, the nut  7  is often disengaged from the bolt  5  by vibrations, an impact and the like during the transport of the battery terminal  4 , and the nut  7  need to be again attached to the bolt, and in some cases the nut is lost. 
     Therefore, there has been proposed a nut disengagement prevention structure (disclosed, for example, in JP-A-10-61647) for preventing the disengagement of a nut from a bolt, in which an E-ring or a retaining cap is fitted on a distal end of the bolt, or an internal thread portion is formed in the distal end of the bolt, and a small screw, having a head larger in diameter than a thread ridge, is threaded into this internal thread portion, or an enlarged-diameter portion is formed at the distal end of the bolt by an expanding slot or a stamped section. 
     Another nut disengagement prevention structure is provided by coating, for example, a coating material, an adhesive or the like onto the distal end of the bolt. 
     In the above nut disengagement prevention structures, however, the pre-processing step for the bolt or the post-processing step, such as the operation for attaching the retaining member to the bolt after the bolt is threaded into the nut, the diameter-enlarging operation, or the coating operation, is added, and therefore there were encountered problems that the mounting operation is troublesome, and required much time and labor, and that the production cost increased because of the increased number of the component parts. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a nut disengagement prevention structure and a battery terminal incorporating the same, in which the disengagement of a nut can be easily prevented with the simple structure. 
     In order to achieve the above object, according to the present invention, there is provided a nut disengagement prevention structure comprising: 
     a bolt, having an external thread; and 
     a nut, thread on the bolt, having an internal thread; 
     wherein the thread portion which is the closest to a leading end of the bolt has a first minor diameter; 
     wherein any other portion of the thread of the bolt has a second minor diameter which is smaller than the first minor diameter; and 
     wherein the second minor diameter is substantially identical with a minor diameter of the internal thread of the nut. 
     In this construction, when the bolt is tightened relative to the nut with a turning torque of above a predetermined value, the nut is threaded toward a proximal end of the bolt, while an internal thread of the nut and the thread portion which is the closest to a leading end of the bolt, engaged with each other, are resiliently deformed. 
     The second minor diameter of the any other portion of the thread of the bolt is substantially identical with the minor diameter of the internal thread of the nut, and therefore an ordinary tightening operation can be effected. 
     Therefore, the nut, once threaded onto the proximal end of the bolt, is held against withdrawal from the bolt unless a turning torque of above a predetermined value is artificially exerted on the nut. 
     According to the present invention, there is also provided a nut disengagement prevention structure comprising: 
     a bolt, having an external thread; and 
     a nut, thread on the bolt, having an internal thread; 
     wherein the thread portion which is the closest to a leading end of the bolt has a first major diameter; 
     wherein any other portion of the thread of the bolt has a second major diameter which is smaller than the first major diameter; and 
     wherein the second major diameter is substantially identical with a major diameter of the internal thread of the nut. 
     In this construction, when the bolt is tightened relative to the nut with a turning torque of above a predetermined value, the nut is threaded toward a proximal end of the bolt, while an internal thread of the nut and the thread portion which is the closest to a leading end of the bolt, engaged with each other, are resiliently deformed. 
     The second major diameter of the any other portion of the thread of the bolt is substantially identical with the major diameter of the internal thread of the nut, and therefore an ordinary tightening operation can be effected. 
     Therefore, the nut, once threaded onto the proximal end of the thread portion of the bolt, is held against withdrawal from the bolt unless a turning torque of above a predetermined value is artificially exerted on the nut. 
     According to the present invention, there is also provided a nut disengagement prevention structure comprising: 
     a bolt, having an external thread; and 
     a nut, thread on the bolt, having an internal thread; 
     wherein adjacent thread portions which are closest to a leading end of the bolt are provided with a first pitch; 
     wherein each of any other adjacent thread portions of the bolt are provided with a second pitch which is different from the first pitch; and 
     wherein the second pitch is substantially identical with a pitch of each adjacent thread portions of the nut. 
     In this construction, when the bolt is tightened relative to the nut with a turning torque of above a predetermined value, the nut is threaded toward a proximal end of the bolt while an internal thread of the nut and the thread portion which is the closest to the leading end of the bolt, engaged with each other, are resiliently deformed. 
     The second pitch each of the any other adjacent thread portions of the bolt is substantially identical with the pitch of each adjacent thread portions of the nut, and therefore an ordinary tightening operation can be effected. 
     Therefore, the nut, once threaded onto the proximal end of the thread portion of the bolt, is held against withdrawal from the bolt unless a turning torque of above a predetermined value is artificially exerted on the nut. 
     Namely, in the bolt having the above nut disengagement prevention structures, only the thread portion which is the closest to the leading end of the bolt need to be formed into a thread configuration slightly different from the specification dimension during an ordinary bolt-producing process, and any special pre-processing step, such as the formation of an expanding slot or a stamped portion at the distal end of the bolt, and any post-processing step, such as the mounting of a retaining member, as used in the related technique, are not necessary, and the number of the component parts will not increase. 
     Therefore, there can be provided the inexpensive nut disengagement prevention structure in which the disengagement of the nut can be easily prevented with the simple structure. 
     According to the present invention, there is also provided a battery terminal comprising: 
     a connection member, fitted with a battery post of a battery; 
     a pair of clamping portions, extended respectively from both ends of the connecting portion; 
     a bolt, having an external thread; and 
     a nut, thread on the bolt, having an internal thread; 
     wherein the thread portion which is the closest to a leading end of the bolt has a first minor diameter; 
     wherein any other portion of the thread of the bolt has a second minor diameter which is smaller than the first minor diameter; and 
     wherein the second minor diameter is substantially identical with a minor diameter of the internal thread of the nut. 
     According to the present invention, there is also provided a battery terminal comprising: 
     a connection member, fitted with a battery post of a battery; 
     a pair of clamping portions, extended respectively from both ends of the connecting portion; 
     a bolt, having an external thread; and 
     a nut, thread on the bolt, having an internal thread; 
     wherein the thread portion which is the closest to a leading end of the bolt has a first major diameter; 
     wherein any other portion of the thread of the bolt has a second major diameter which is smaller than the first major diameter; and 
     wherein the second major diameter is substantially identical with a major diameter of the internal thread of the nut. 
     According to the present invention, there is also provided a battery terminal comprising: 
     a connection member, fitted with a battery post of a battery; 
     a pair of clamping portions, extended respectively from both ends of the connecting portion; 
     a bolt, having an external thread; and 
     a nut, thread on the bolt, having an internal thread; 
     wherein adjacent thread portions which are closest to a leading end of the bolt are provided with a first pitch; 
     wherein each of any other adjacent thread portions of the bolt are provided with a second pitch which is different from the first pitch; and 
     wherein the second pitch is substantially identical with a pitch of each adjacent thread portions of the nut. 
     In the constructions, the bolt and the nut, beforehand connected to the battery terminal in an integrated manner, will not be disengaged from each other by vibrations, an impact or the like during the transport before this battery terminal is fed to a production line where the nut and the bolt are finally completely fastened together. 
     Therefore, the battery terminal, incorporated with the bolt and the nut connected thereto in an integrated manner, can be positively stored as one part, and the cost for the parts management can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
     FIG. 1 is an enlarged, cross-sectional view showing an important portion of one preferred embodiment of a nut disengagement prevention structure of the present invention; and 
     FIG. 2 is a perspective view showing the structure of mounting a battery terminal on an electrode of a battery. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One preferred embodiment of a nut disengagement prevention structure according to the present invention will now be described bellow in detail with reference to the accompanying drawings. 
     Dimensions of a bolt  10  of this embodiment are so determined that a root diameter (minor diameter) d 1  of an external thread  10   a  at a distal end of a thread portion of the bolt  10  is larger than a root diameter d 2  of an external thread  10   b  at a proximal-side portion (left side portion in FIG. 1) of the thread portion of the bolt, as shown in FIG.  1 . 
     A nut  12  for being threaded on the bolt  10  has an internal thread  12   a  having an inner diameter D 2  corresponding to the root diameter d 2  of the external thread  10   b  at the proximal-side portion of the thread portion of the bolt  10 . 
     The root diameter d 1  of the external thread  10   a  at the distal end of the thread portion of the bolt  10  is larger than the inner diameter D 2  of the internal thread  12   a  of the nut  12  for being threaded on the bolt  10 , and the external thread  10   a  is formed into such a slightly-different thread configuration as to provide a tighter threaded engagement as compared with the root diameter d 2  (which is the proper specification dimension) of the external thread  10   b  (at the proximal-side portion of the thread portion) corresponding to the internal thread  12   a  of the nut  12 . 
     Namely, when the bolt  10  is tightened relative to the nut  12  with a turning torque of above a predetermined value, the nut  12  is threaded toward the proximal-side portion of the thread portion of the bolt  10  while the crest of the internal thread  12   a  is resiliently deformed at a root R of the external thread  10   a  at the distal end of the thread portion of the bolt. Then, when the internal thread  12   a  of the nut  12  reaches the external thread  10   b  at the proximal-side portion of the thread portion of the bolt  10 , the threaded condition of the nut  12  and bolt  10  becomes normal. 
     Therefore, the nut  12 , once threaded onto the proximal-side portion of the thread portion of the bolt  10 , is held against withdrawal from the bolt  10  unless a turning torque of above the predetermined value is artificially exerted on the nut  12 . 
     Therefore, for example, in the case of the battery terminal  4  (shown in FIG. 2) in which the nut is beforehand loosely tightened relative to the bolt, if a battery terminal, having the bolt  10  and the nut  12  connected thereto in an integrated manner, is used instead of using the related bolt  5  and nut  7 , the nut  12  will not be disengaged from the bolt  10  by vibrations, an impact or the like during the transport, and the nut  12  does not need to be again attached to the bolt, or will not be lost. 
     Therefore, the battery terminal, having the bolt  10  and the nut  12  connected thereto in an integrated manner, can be positively stored as one part, and the cost for the parts management can be reduced. 
     The root diameter d 2  of the external thread  10   b  at the proximal-side portion of the thread portion of the bolt  10  is the specification dimension corresponding to the inner diameter D 2  of the internal thread  12   a  of the nut  12 . For example, in the case where the battery terminal, having the bolt  10  and the nut  12  beforehand connected thereto in an integrated manner as described above, is fed to the production line, and is finally completely fastened to the electrode, this fastening operation can be carried out totally in the same manner as the ordinary fastening operation. 
     In the bolt  10  having the structure for preventing the disengagement of the nut  12 , it is merely necessary to produce this bolt  10  during an ordinary production process in such a manner that only the root diameter d 1  of the external thread  10   a  at the distal end of the thread portion is slightly longer than the root diameter d 2  (which is the specification dimension) of the external thread  10   b  at the proximal-side portion of the thread portion, and any special pre-processing step, such as the formation of an expanding slot or a stamped portion at the distal end of the bolt, and any post-processing step, such as the mounting of a retaining member, as used in the conventional technique, are not necessary, and the number of the component parts will not increase. 
     Therefore, the production cost will not increase, and the disengagement of the nut can be easily prevented with the simple structure. 
     In the above embodiment, the root diameter d 1  of the external thread  10   a  at the distal end of the thread portion of the bolt  10  is larger than the root diameter d 2  (which is the proper specification dimension) of the external thread  10   b  at the proximal-side portion of the thread portion, and with this construction, the external thread  10   a  is formed into such a slightly-different thread configuration as to provide a tighter threaded engagement relative to the inner diameter D 2  of the internal thread  12   a  of the nut  12 . However, the nut disengagement prevention structure of this invention is not limited to this embodiment, and within the scope of the invention, the distal end of the thread portion of the bolt can be formed into any other suitable, slightly-different thread configuration which can provide a tighter threaded engagement relative to the internal thread of the nut. 
     In FIG. 1, for example, the outer diameter d 4  of the external thread  10   a  at the distal end of the thread portion of the bolt  10  may be made larger than the outer diameter d 3  (the proper specification dimension) of the external thread  10   b  at the proximal-side portion of the thread portion, or the pitch P 1  of the external thread  10   a  at the distal end of the thread portion of the bolt  10  may be made larger or smaller than the pitch P 2  (the proper specification dimension) of the external thread  10   b  at the proximal-side portion of the thread portion, and by doing so, the distal end of the thread portion of the bolt  10  can be formed into such various slightly-different thread configurations as to provide the tighter threaded engagement relative to the internal thread  12   a  of the nut  12 . 
     The nut disengagement prevention structure of the present invention is not limited to the bolt-nut assembly for the above battery terminal, but can be applied to any other suitable bolt-nut assembly in so far as the nut can be beforehand provisionally mounted on the bolt.