非对称结构形式的不完全齿轮机构设计

Asymmetrical form of Incomplete Gear Mechanism

不完全齿轮常采用停止位时从动轮齿形对称分布,同时降低主动轮首末齿齿高的方法进行设计。为避免重合度小于1,这种方法需要的主从动齿轮全齿数较多。提出了停止位时从动轮齿形非对称布置的设计方法,推导了设计计算公式,画出了首对齿与第二对齿的重合度分布图、始啮和脱啮位置的角加速度图。通过分析表明,选择标准齿高两齿轮齿顶的啮出区交点作脱齿定位点,可保证啮入和啮出刚性冲击较小,并使机构完全避免产生二次冲击。锁止弧位置灵活,使从动轮锁止弧弧长不再受限于首末齿驱动转过的齿数K值,可用作主从动轮的全齿数可以比较少,结构更加紧凑;主动轮末齿齿顶高不必降低,从动轮可采用全齿轮。

The methodology for designing the incomplete gear is supposed that the configuration of the tooth distribution on the driven gear at stationary location is symmetrical to the center line of the meshing gears and the addenda of the first and last teeth in driving gear should be reduced symmetrically, and a engineer should choose the more numbers of teeth on the complete gears for preventing the contact ratio being less than one. A new methodology is proposed to design the form of asymmetrical configuration of the teeth distribution on the driven gear at stationary location and its design formulae are derived from the geometrical positior~ The contour maps reflecting the contact ratio between the first pair and the next pair of teeth and the curves expressing the relationship between the stationary locations of the driven gear and its angular accelerations at beginning and leaving point of contact are drawn. Analyses show that choosing the intersection between the addendum circles at mesh out side as the stationary location of driven gear can be kept the rigid impulse occurred at the beginning and leaving point of contact in the proper smaller values, and the impulse secondly occurred during the mesh is completely avoided. The positions of locking arcs can be flexibly chosen, and the arc segment of a locking arc on driven gear is no longer limited to the K value ,which is the tooth number of driven gear contained in the arc between the two intersections of the addendum circles. The smaller numbers of gears when fuUy filled with teeth to forming complete gears, therefore, can be chosen as candidates and the smaller dimension of the mechanism may be designed. The addendum of the last tooth on driving gear should be not reduced and the driven gear may be the complete gear.