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Engineering Tribology Episode 2 Part 6

Tham khảo tài liệu 'engineering tribology episode 2 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 350 Engineering Tribology temperature 56 and this characteristic cannot be neglected in any model of EHL with sliding present. EHL Between Meshing Gear Wheels From the view point of practical engineering an important EHL contact takes place between the lubricated teeth of opposing gears. As is the case with rolling bearings it is essential to maintain an adequate EHL film thickness to prevent wear and pitting of the gear teeth. The same fundamental equations for EHL film thickness described for a simple Hertzian contact also apply for gears. However before applying the formulae for contact parameters and minimum film thickness it is necessary to define reduced radius of curvature contact load and surface velocity for a specific gear. The contact geometry is illustrated in Figure 7.42. Figure 7.42 Contact geometry of meshing involute gear teeth. The surface contact velocity is expressed as ư UA UB ARAsin y BRBsin y 2 2 where Ra Rb are the pitch circle radii of the driver and follower respectively m y is the pressure angle acute angle between contact normal and the common tangent to the pitch circles I A I are the angular velocities of the driver and follower respectively rad s . Since Ra _ B Rb 0 a Then the contact surface velocity is TEAM LRN Elastohydrodynamic Lubrication 351 U o aRaSIU o BRBsiny 7.53 Assuming that the total load is carried by one tooth only then from Figure 7.42 the contact load in terms of the torque exerted is given by W TB Tb hB RbCOS 7.54 where W is the total load on the tooth N hB is the distance from the centre of the follower to interception of the locus of the contact with its base circle i.e. hB RBcosy m TB is the torque exerted on the follower Nm . The torque exerted on the driver and the follower expressed in terms of the transmitted power is calculated from T ta OA - T tb o -N B B where Na Nb are the rotational speeds of the driver and follower respectively rps H is the transmitted power kW . Substituting into 7.54 yields the contact