Research On A Pair Of Metal Worm And Plastic Gear With Unequal Pitch

Compared with ordinary worm gear pair,the transmission mode of metal worm and plastic gear has the characteristics of simple processing.It is widely used in the fields of automobile,household appliances,smart home and medical machinery.In recent years,the requirements for the bearing capacity and transmission stability of plastic gears meshing with metal worm are higher and higher.For example,such as window lift and wiper,they require small volume,large bearing capacity and good stability.The bearing capacity of conventional plastic gears is difficult to meet the requirement.Although the strength of the reinforced plastic gear modified with glass fiber or carbon fiber increases,It also has its shortcomings.According to the traditional design method,the normal tooth pitch of worm and gear is equal.In this paper,the meshing transmission characteristics of unequal pitch worm with gear(UPWG)are studied by matching metal worm and plastic gear.In this transmission mode,the pitch of the metal worm is not equal to that of the plastic gear(the tooth pitch of the worm is less than that of the plastic gear).By balancing the tooth root bending stress of the plastic gear,the bearing capacity of the meshing pair of the worm and the plastic gear is improved,the stability of the transmission is improved and the service life is increased.The research of UPWG meshing transmission has important theoretical and application value for improving the bearing capacity of metal worm and plastic gear transmission system and improving the transmission stability.The research contents of this paper include:(1)The type of UPWG transmission and its design and calculation method are proposed.In order to improve the bearing capacity of plastic gear transmission system,a new UPWG gear pair for meshing transmission is proposed,which makes the bending stress of plastic gear tooth root equal through parameter optimization design,so as to optimize the meshing transmission characteristics.Therefore,it is necessary to calculate the load and contact deformation of EPWG,give the definition of bending deformation rate at the tooth root of plastic gear,and obtain the tooth root bending deformation rate when a single tooth of plastic gear bears the maximum load in EPWG meshing;Aiming at the balance of bending stess of plastic gear root,the design method of worm gear unequal pitch transmission system is calculated,and the calculation method of contact ratio and sliding rate of UPWG meshing are further studied.(2)The calculation and analysis of tooth root bending stress and contact stress of plastic gear with UPWG transmission mode are studied.Aiming at the stress analysis of plastic gear in UPWG meshing under load,the stress of plastic gear is calculated by analytical method and finite element method,and a new algorithm for calculating the bending stress of plastic gear tooth root is proposed.The algorithm solves the problem of calculating the bending stress of plastic gear tooth root when the tooth root transition curve is circular arc.The results show that the analytical method is consistent with the finite element calculation.Based on the new algorithm,the effect of UPWG mode on balancing the bending stress of the tooth root of meshing teeth is verified.The data show that the balanced distribution of bending stress of each tooth of metal worm and plastic gear under UPWG mode is obviously better than that of EPWG mode.The applicable range of UPWG meshing mode is further calculated,and it is concluded that the smaller the modulus of plastic gear and the greater the load,the more significant the effect of applying UPWG mode.(3)The gear pair pitch deviation and meshing characteristics of EPWG and UPWG transmission modes are studied.Firstly,the meshing impact type of EPWG gear pair is analyzed based on the idea of overall error of gear pair;Secondly,the meshing impact types of UPWG metal worm and plastic gear are analyzed,and the influence of gear pair pitch deviation of two transmission modes on meshing impact is compared and analyzed;Finally,the gear tooth alternating curves of the two transmission modes under no-load and load conditions are given respectively,and the mechanism of more stable UPWG transmission under specific conditions is explained.(4)The dynamic characteristics of UPWG transmission system are analyzed.Aiming at the transmission stability of UPWG meshing transmission under large load,the contact force and transmission error between worm and gear are studied with speed and load as variables,and the rigid body and flexible body modeling,contact stiffness calculation and simulation analysis of UPWG system are carried out.The results show that for the plastic gear and metal worm transmission system,UPWG is better than EPWG.The fluctuation range of tooth surface contact force and transmission error of UPWG is small,and the UPWG transmission is more stable under large load.(5)Experimental study on UPWG transmission.The static strength experiment and dynamic stability experiment of the proposed UPWG meshing transmission mode are carried out,and the experimental data are compared and analyzed.The experimental results show that compared with EPWG mode,the bearing capacity of UPWG transmission is effectively improved.The current stability and vibration test of gearbox motor show that the stability of gear on load transmission is improved and the bearing capacity of gear pair is improved.Experiments verify the effectiveness and feasibility of UPWG meshing transmission mode.