Tham khảo tài liệu 'dynamics of mechanical systems 2009 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 582 Dynamics of Mechanical Systems FIGURE Meshing involute spur gears determining the pitch circles. FIGURE Profile of meshing gear teeth. Unlike the root circle the base circle and the addendum circle the pitch circle is not fixed relative to the tooth. Instead the pitch circle is determined by the center distance between the mating gears. Hence the addendum dedendum and tooth thickness may vary by a small amount depending upon the specific location of the pitch circle. The location of the pitch circle on a gear tooth is determined by the location of the point of contact between meshing teeth on the line connecting the gear centers as illustrated in Figure . An advantageous property of involute spur gear tooth geometry is that the gears will operate together with conjugate action at varying center distances with only the provision that contact is always maintained between at least one pair of teeth. Next consider a closer look at the interaction of the teeth of meshing gears as in Figure . If the gears are not tightly pressed together there will be a separation between noncontacting teeth. This separation or looseness is called the backlash. The distance measured along the pitch circle between corresponding points on adjacent teeth is called the circular pitch. Circular pitch is commonly used as a measure of the size of a gear. From Figure we see that even with backlash unless two gears have the Mechanical Components Gears 583 Figure Perspective view of a spur gear tooth. same circular pitch they will not mesh or operate together. If a gear has N teeth and a pitch circle with diameter d then the circular pitch p is p nd N Another commonly used measure of gear size is diametral pitch P defined as the number of teeth divided by the pitch circle diameter. That is P N d Usually the diametral pitch is computed with the pitch circle diameter d measured in inches. Still another measure of gear size is the module m .
