1050000 1 n KN i i A A tx Ψ σ 838 Nh� vaäy töø ñieàu kieän beàn tieáp xuùc ta

1050000 1 n kn i i a a tx ψ σ 838 nh? vaäy töø

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. . ] [ 1050000 ) 1 ( n KN i i A A tx Ψ σ + (8.38) Nhö vaäy töø ñieàu kieän beàn tieáp xuùc ta ñònh ñöôïc A, moâ ñun aên khôùp vaø soá raêng coù theå coù caùc trò soá khaùc nhau chæ caàn thoaû maõn: 1 2 2 1 2 ) ( z z i vaø A z z m = = + Kieåm tra beà maët raêng bò quaù taûi ñoät xuaát theo [ σ ] txq : txq q tx txq M M ] [ . 1 1 σ σ = σ (8.39) 8.2.3.1.2. Ñoái vôùi baùnh raêng truï raêng nghieâng a) Löïc taùc duïng taïi vò trí aên khôùp: ÔÛ boä truyeàn baùnh raêng nghieâng löïc phaùp tuyeán P n taïo vôùi maët ñaàu muùt moät goùc β . Phaân tích P n ra thaønh caùc thaønh phaàn: Q T P P n G G G G + + = - Löïc voøng P G : = = ) ( 2 2 2 2 1 1 r vaø quay truïc P d M d M P G G (8.40) - Löïc höôùng taâm T G : α β = α = taâm höôùng T tg P tg S T G . cos . (8.41) - Löïc doïc Q G : β = truïc Q tg P Q // . G (8.42) Khi xaùc ñònh chieàu caùc löïc phaûi chuù yù ñeán cheàu quay cuûa baùnh raêng vaø chieàu nghieâng cuûa raêng (phaûi hay traùi).
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Giaùo Trình CÔ HOÏC ÖÙNG DUÏNG CHÖÔNG 8. TRUYEÀN ÑOÄNG BAÙNH RAÊNG 181 Löïc doïc taùc duïng theâm taûi troïng vaøo oå, Q taêng cuøng vôùi goùc β . Vì vaäy, ñoái vôùi baùnh raêng nghieâng thöôøng β = 8 ÷ 15 o .Toàn taïi löïc truïc laø moät nhöôïc ñieåm cuûa baùnh raêng nghieâng. b) Nhöõng thoâng soá hình hoïc chuû yeáu cuûa baùnh raêng: Maët phaùp – tieát dieän phaùp – laø maët phaúng chöùa T vaø S G G . Tieát dieän ngang laø maët phaúng vuoâng goùc vôùi truïc. Goïi t n , m n : böôùc raêng, moâ ñun trong tieát dieän phaùp. t s , m s : böôùc raêng, moâ ñun trong tieát dieän ngang. Ta coù quan heä: β = β = cos ; cos n s n s m m t t Ñöôøng kính voøng chia: d c = m s .z = β cos z m n (8.43) Caùc kích thöôùc chieàu cao raêng, ñöôøng kính voøng ñænh vaø voøng ñaùy raêng xaùc ñònh theo caùc coâng thöùc nhö cuûa baùnh raêng thaúng, vôùi chuù yù laø thay m baèng m n . Khoaûng caùch truïc trong boä truyeàn baùnh raêng nghieâng tieâu chuaån hay dòch chænh ñeàu: β + = cos . 2 2 1 n m z z A (8.44) c) Tính toaùn boä truyeàn hôû baùnh raêng truï raêng nghieâng coù moät soá caëp raêng ñoàng thôøi vaøo aên khôùp, neân laøm giaûm taûi troïng treân moät raêng, do ñoù naâng cao ñoä beàn cuûa noù. Caùc raêng nghieâng laøm taêng ñoä cöùng cuûa noù khi uoán, giaûm bôùt taûi troïng ñoäng,… Xeùt ñeán ñoä beàn cuûa baùnh raêng nghieâng tieán haønh theo caùc coâng thöùc cuûa boä truyeàn baùnh raêng thaúng töông ñöông vaø ñöa vaøo noù caùc coâng thöùc ñieàu chænh. Theo ñieàu kieän beàn, kích thöôùc cuûa boä truyeàn baùnh raêng nghieâng nhoû hôn so vôùi baùnh raêng thaúng.
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