（I）Calculation of Ｐ0 Ｐ0 ＝ＦecＶ／1000 → Max. power of single V-belt
Ｆec≤Ｆ1（1－1／ｅfva ） → don’t slip Ｆ1 ＝σ1A σ1≤[σ]－σb1－σc → ensure enough fatigue strength
∴ Max. power P0 of single v-belt: Ｐ0＝([σ]－σb1－σc)Ａ(1－1／ｅfva )Ｖ／1000ｋｗ （II）Basic rating powerＰ0 of single v-belt (specified cond.) 1.Ｐ0: Based on dd1, ｎ1 and types→search Table 8-4a 2. Specified cond.： ①steady load ②wrap angle α1=π（ｉ=1）; ③specified length
3. Modified coefficient in unspecific cond.
①Service factor ＫA → 非平稳载荷ＫA ＞ 1
②wrap angle factorＫα: Table 8-8 当α1＜π →承载力↓→Ｋα＜ 1→α1 ↓ →Kα↓ ③Length factorＫL : Table 8-2 When L＞specific length→rotation number N ↓→transmission power↑→ＫL ＞1 When L＜specific length→ＫL ＜ 1
Exercises
• 8-1 and 8-4 on page 164 Notice: in problem 8-4, you should design both V belt and belt wheel. (设计V带和带 轮).
Table 8-6
4. Power increment△P0 of single v-belt (Table 8-4b) Whenｉ＞1→dd2↑→σb2 ↓→bearing capacity↑→transmission power↑→ △P0 ＞0
III. Permissible power [Ｐ0] of single v-belt Permissible power：[P0]= (P0+△P0) KαKL Total power：Pca = KA P Number of v-belt： Z= Pca / [P0] IV. Design calculation of v-belt transmission 1. Design method： Known：Ｐ, ｎ, ｉ and Working condition Selection：Types, dd, Ｌd, a=(0.7~2)(dd1+dd2) Solve: 1. Ｚ＝Ｐca／[Ｐ0] 2. F (Forces acting on a shaft） Check：V , α 1≥120°（at least 90°）
计算 Pca =-11
2 . V带传动的设计步骤
选择dd
计算Ｌd 、 a
——套基准直径 表8-8
验算V 1≤15m／s
——套基准长度 表8-2
验算 α 1≥120°
带根数 Z= Pca / [P0]——取整数
计算预紧力F0，压轴力Fp
设计带轮 ——画零件工作图
§8—3 Ｖ-belt drive design
I. Failure type and design criterion ☆Failure type ★ design criterion
When Ｆe＞Ｆfmax＝Ｆec →打滑
Ｆe≤Ｆec
When σmax＞[σ] →endurance falure σmax≤[σ] σ1≤[σ]－σb1－σC
Design criterion： Prevent belt from slipping, and ensure enough fatigue strength and life. Design method： [Ｐ0] → Ｚ＝Ｐca／[Ｐ0]
II. Basic rating powerＰ0 of single V-belt