Research On Key Technologies Of Steel Planar Wormgear Enveloping Hourglass Worm Gears

The precision worm gears, which is used as a precision indexing or a fine motion mechanism, mainly uses in gear cutting machine, accuracy machine tool with indexing function, precision rotary table or instruments, and so on. Researching on the precision-power worm drives which can satisfy the higher input speed, the greater output torque, the smaller teeth clearance, the better rigidity, the longer accuracy life, etc, has the vital practical significance. The steel variational-tooth-thickness planar wormgear enveloping hourglass worm drive can satisfy the dual requirements of"precision"and"power". How to design, manufacture and guarantee its tribology performances are the key technologies to achieve this transmission successfully. This dissertation investigates the key technologies such as meshing theory, parametric analysis, tooth contact analysis, precision machining, elastohydrodynamic lubrication (EHD) analysis, material combinations test, trial manufacture, and so on.The mesh theory of the planar worm gears is presented based on the differential geometry and the conjugate curved-surface principle. Influences of main parameters such as slope angle of generitix, pressure angle, axial module, etc. on distribution of contact lines, undercut of worm, and tooth thickness of wormgear, are studied on considering the characteristics of the new transmission. On the basis of engagement analysis together with technology analysis of machining and assembling, tooth surfaces models and assembly model containning errors are established. The tooth contact analysis of the driven are carried on by using the teeth-surface-clearance method. Effects of errors on teeth contact state are studied. General suggestions are proposed to minimizing the disadvantage effects of errors, and modifying the profile of the worm.Based on explaining the generating theory of planar enveloping hourglass worm, the principle of dummy gyration center is demonstrated by the knowledge of plane kinematics of rigid body. Machining test is carried out and the feasibility of the new principle is identified further. The results show that the dummy gyration center can be used in machining the hourglass worm completely, and the numeric control machine tool with the function of the dummy gyration center has versatile characteristic to processing all kinds of worm components.Through the processing method analysis and processing test, the cutting methods of planar wormgear such as milling, slotting, fly-cutting, grinding, and hobbing are discussed. The fly cutting method is studied further and the mathematical model of fly cutting is established by the method of moving coordinate. Error analysis, optimization design, analog simulation and technique test are carried out. The suitable situation, merits and faults of the cutting methods are presented.Based on study of EHD and mesh theory of the steel planar worm gears, EHD model for the drive is proposed. Minimum film thickness on the whole contact area is calculated. The distributions of film thickness are analyzed. Influences of velocity, load, slope angle of generitix, pressure angle and reference diameter of worm on lubrication performance are investigated. The results show that, the EHD status during entry engagement is better than that during exit engagement, and EHD state of worm addendum area is better than that of dedendum area. Optimizing pressure angle and increasing worm reference diameter have effect on improving lubrication performance. The influences of the variable on the transmission efficiency, frictional wear should be considered too during improving lubricantion.Based on study of tribology performances of the drive, the steel-steel line-contact sliding-friction model is established to simulate the tribology system of arbitrary contact point. Influencing factors along with their effects are analyzed. The results show that, extreme pressure gear oil containing more additive is suitable for steel-steel sliding friction pair, lubrication oil with high viscosity is beneficial to sliding friction higher pair, the larger relative curvature radius of sliding pair leads to lower friction coefficient in smooth conditions, the larger lubrication angle has higher advantageous to minimizing friction factor, the roughness of surfaces is vital in thin oil film conditions, nitration case can avoid excessive wear effectively, the recommended techniques of heat treatment are nitrogen treatment vs nitrogen treatment and nitrogen treatment vs carbonization, the friction pair which have high surface hardness and low difference of hardness has excellent wear resisting property.Steel variational-tooth-thickness planar worm gears is designed on considering the mentioned above findings. Two pairs of worm gears are trial manufactured using two material combinations.The dissertation is supported by National Natural Science Foundation(50075089).