Pulley and string arrangement structure of bow

Abstract

A pulley and string arrangement structure of a bow contains a bow body, an arm assembly, two pulleys, a string fixer, a main string, two first auxiliary strings, and two second auxiliary strings. The bow body includes an arrow-receiving portion. The arm assembly is mounted on the bow body and extends from the bow body. A respective one pulley includes a main string layer, a first and second retraction units, a first and second defining portions, a first and second expansion units, and a first and second locating portions. The main string layer has a guide grove and a positioning portion. The first and second retraction units include a first and second guiding slots. The first and second expansion units include a first and second conduct slots. A center of the arm assembly and the main string layer has a virtual datum plane.

What is claimed is: 
     
         1 . A pulley and string arrangement structure of a bow comprising: a bow body, an arm assembly, two pulleys, a string fixer, a main string, two first auxiliary strings, and two second auxiliary strings; wherein
 the bow body includes an arrow receiving portion formed on a top thereof and configured to hold an arrow;   the arm assembly is mounted on the bow body and extends from two sides of the bow body;   the two pulleys are symmetrical and rotatably connected on two ends of the arm assembly, wherein a respective one pulley includes a main string layer, a first and second retraction units and a first and second defining portions which protrude from a top and a bottom of the main string layer, a first and second expansion units and a first and second locating portions which are located on tops and bottoms of the first and second retraction units;   the main string layer has a guide grove defined on an outer side thereof, and a positioning portion formed in the main string layer;   the first and second retraction units include a first and second guiding slots defined on outer walls of the first and second retraction units, wherein the first guiding slot corresponds to the first defining portion, and the second guiding slot corresponds to the second defining portion;   the first and second expansion units include a first and second conduct slots, the first conduct slot corresponds to the first locating portion, and the second conduct slot corresponds to the second locating portion;   a center of the arm assembly and the main string layer has a virtual datum plane extending along the arrow body, and the virtual datum plane parallel to a center of the first retraction unit has a virtual first top plane, a bottom of the virtual datum plane parallel to a center of the second retraction unit has a virtual first bottom plane, the virtual first top plane parallel to a center of the first expansion unit has a virtual second top plane, and a bottom of the virtual first bottom plane parallel to a center of the second expansion unit has a virtual second bottom plane;   the string fixer is fixed on the bow body adjacent to the arm assembly, and the string fixer includes a first guide roller and a second guide roller which are mounted on two sides of the string fixer;   the main string rolls in the two guide groves of the two pulleys via two sides of the bow body, and two ends of the main string move into two recesses to connect with the two positioning portions, such that the main string is located on the virtual datum plane;   an end of the respective one first auxiliary string is fitted with the respective one first defining portion and is rolled in the first guiding slot of the first retraction unit, in the meantime, the respective one first auxiliary string is the virtual first top plane, and the other end of the respective one first auxiliary string is fitted with the first locating portion and is rolled in the first conduct slot of the first expansion unit, in the meantime, the respective one first auxiliary string is the virtual second top plane, and a middle section of the respective one first auxiliary string passes through the first guide roller;   an end of the respective one second auxiliary string is fitted with the respective one second defining portion and is rolled in the second guiding slot of the second retraction unit, in the meantime, the respective one second auxiliary string is the virtual first bottom plane, and the other end of the respective one second auxiliary string is fitted with the second locating portion and is rolled in the second conduct slot of the second expansion unit, in the meantime, the respective one second auxiliary string is the virtual second bottom plane, and a middle section of the respective one second auxiliary string passes through the second guide roller;   a front end of the main string is not strung, and the min string is drawn backward to be strung, wherein when not stringing, a length of the respective one first auxiliary string and the respective one second auxiliary string located in the first guiding slot and the second guiding slot is shorter than a length of the respective one first auxiliary string and the respective one second auxiliary string which are strung; when not stringing, a length of the respective one first auxiliary string and the respective one second auxiliary string located in the first conduct slot and the second conduct slot is longer than a length of the respective one first auxiliary string and the respective one second auxiliary string which are strung; when desiring to string to shoot the arrow, the main string is drawn backward to be deformed so that the length of the respective one first auxiliary string and the respective one second auxiliary string located in the first guiding slot and the second guiding slot and the length of the respective one first auxiliary string and the respective one second auxiliary string located in the first conduct slot and the second conduct slot are changeable to store an energy by using a potential energy change, and when releasing the main string, an elastic energy storage of the arm assembly curvedly deforms and an energy storage of the first retraction unit and the second retraction unit are released simultaneously via the main string to release.   
     
     
         2 . The pulley and string arrangement structure as claimed in  claim 1 , wherein the two pulleys are rotatably connected on the two ends of the arm assembly by using two shafts. 
     
     
         3 . The pulley and string arrangement structure as claimed in  claim 1 , wherein the main string layer has the recess defined in the main string layer and communicates with the guide groove, and the first and second retraction units shrink the recess of the main string layer. 
     
     
         4 . The bicycle seat as claimed in  claim 1 , wherein the first and second retraction units are symmetrical, the first and second defining portions are symmetrical, the first and second expansion units are symmetrical, and the first and second locating portions are symmetrical.