Tooth contact must be good under no load.ģ. For double helical gears, b is facewidth including central groove.Ģ. The b means effective facewidth of spur and helical gears. Table 10.11 Longitudinal load distribution factorġ. This case relates to the method of gear shaft support, and to the ratio, b/d01, of the gear facewidth b, to the pitch diameter, d01. When tooth contact under load is not predictable: The longitudinal load distribution factor, KHβ, is obtainable from:ġ. (3)-12 Longitudinal Load Distribution Factor, KHβ If a gear is out of this range, the ZW is assumed to be 1.0.īecause the conditions affecting this parameter are often unknown, the factor is usually set at 1.0. Where HB2:Brinell hardness of gear range: The hardness ratio factor, ZW, is calculated by Equation (10.24).
The hardness ratio factor, ZW, applies only to the gear that is in mesh with a pinion which is quenched and ground. The lubrication speed factor, ZV, relates to the tangential speed of the pitch circle, v (m/s). The average roughness, Rmaxm is calculated by Equation (10.23) using the surface roughness values of the pinion and gear, Rmax1 and Rmax2, and the center distance, a, in mm. The surface roughness factor, ZR is obtained from Figure 10.4 on the basis of the average roughness Rmaxm (μm). NOTE : Thermal refined gears include quenched and tempered gears and normalized gears. The lubricant factor, ZL is based upon the lubricant’s kinematic viscosity at 50 degree Celsius, cSt. When the number of cycles is unknown, KHL is assumed to be 1.0. The duty cycle is the number meshing cycles during a lifetime.Īlthough an idler has two meshing points in one cycle, it is still regarded as one repetition.įor bidirectional gear drives, the larger loaded direction is taken as the number of cyclic loads.
Table 10.10 indicates the life factor, KHL Therefore, it is assumed to be 1.0 unless better information is available. This is a difficult parameter to evaluate. NOTE (1) Structural steels are S ~ C、SNC、SNCM、SCr、SCM etc.Ĭontact ratio factor can be determined from: Table 10.9 contains several combinations of material and their material factor, ZM. The material factor, ZM is determined from:
The “+” symbol applies to external gear meshes, whereas the “-” is used for internal gear and external gear meshes. The zone factors are presented in Figure 10.2 for tooth profiles per JIS B 1701, pressure angle αn = 20°, profile shift coefficient x1 and x2, numbers of teeth z1 and z2, and helix angle β0. Αbs :Working transverse pressure angle (degrees) In order to obtain the values of the allowable forces shown in the dimensional table, the calculations were made based on condition that the facewidth was: When gears are end relieved, the effective facewidth should not include the relieved portions. When gears with wider facewidth mate with gears with thinner facewidth, take thinner the facewidth for the calculation of surface strength bH. (3)-1 Effective Facewidth in Calculating Surface Strength bH(mm) For the case of a gear rack and a gear, the quantity i/i ☑ becomes 1. The “+” symbol in Equations (10.17) and (10.18) applies to two external gears in mesh, whereas the “-” symbol is used for an internal gear and an external gear mesh. The Hertz stress σH(kgf/mm2) is calculated from Equation (10.18) The allowable tangential force, Ft lim (kgf), at the reference pitch circle, can be calculated from Equation (10.17) In order to satisfy the surface durability, the transmitted tangential force at the reference pitch circle, Ft, is not to exceed the allowable tangential force at the reference pitch circle, Ft lim, that is calculated taking into account the allowable Hertz stress.Īt the same time, the actual Hertz stress, σH, that is calculated on the basis of the tangential force at the reference pitch circle, Ft, should not exceed the allowable Hertz stress, σHlim. N :Rotational speed (rpm) (2) Surface Durability Equations V0 :Tangential speed of working pitch circle (m/s) = d0n / 19100 The equations that relate tangential force at the pitch circle, Ft(kgf), power, P(kW), and torque, T(kgf・m) are basic to the calculations.
Rotational speed n 3600rpm or less (1) Conversion Formulas The following equations can be applied to both spur gears and helical gears, including double helical and internal gears, used in power transmission. Surface Durability of Spur and Helical Gears.