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Unformatted text preview: Chapter 7 Worm gearsh ” 5„ “* 1.The differences between worm gears and other gear types 2.Loads exerted on gears (wheels) 3.Failures and materials of worm gears 4. Power rating system for worm gears 5.Options of parameters for worm gears 6.Structure and lubrication of worm gears 1.The differences between worm gears and other gear types 1)Large speed ratio and crossed axles z &9 „ “ To transfer power: i=8~70; To transfer motion: i max =1000 2)selflocking .¡¡¡ When helix angle γ ≤ ϕ v (equivalent frictional angle, z &9 „ “ ), worm gears cann’t be backdriven. η ≤ 50% 3)Sliding velocity: p249 γ π γ cos 1000 60 cos 1 1 1 × = = n d v v s 4) The influence of the siding velocity of worm gears • Lower efficiency .&& When Z 1 =1, η≈ 0.70~0.75; (cann’t be selflocking) Evaluate x ¡9 „ equation: )% 5 . 3 100 ( i = η (714) • Heat generation due to friction requires effective lubrication for the worm—heat balance rating • Adhesive x ¡9 „ wear is primary concerned of worm gears failure type. • The qualities required in the material for worm gears are low friction coefficient and resistance to wear fatigue. Selfstudy: types of worm gears, p237~240 2.Loads exerted on worm gears 1) Loads calculation Friction of meshing cann’t be neglected 1 1 2 1 1 1 2 t t a t F F F d T F μ + ′ = = = 1 2 2 2 2 a t F d T F = = α tg F F F t r r 2 2 1 ≈ = n a n a n F F F α γ α γ cos cos cos cos 1 1 ≈ ′ = η ⋅ ⋅ = i T T 1 2 γ μ ctg F F F F F t a a a a ⋅ ′ = ′ + ′ = 1 1 1 1 1 , 20 = α 2)The efficiency of worm gears transmission η 3 2 1 η η η η ⋅ ⋅ = Where: Meshing efficiency ) 13 7 ( ) ( 1 = γ ϕ γ η tg tg v ) 12 7 ( ) ( 1 + = v tg tg ϕ γ γ η 96 . ~ 95 ....
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This note was uploaded on 10/26/2010 for the course MECHANICAL 072203 taught by Professor Zhangying during the Spring '06 term at Tsinghua University.
 Spring '06
 ZhangYing

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