上帝充通大￥ Shanghai Jiao Tong University Basic Belt Drives2 Ae! VX<VB<VI Except for timing belts,there is some slip and creep 弹性滑动)，so the angular-.velocity between the driving and driven shaft is neither constant nor exactly equal to the ratio of the pulley diameters. 6
6 Basic Belt Drives2 Except for timing belts, there is some slip and creep（ 弹性滑动）, so the angular-velocity between the driving and driven shaft is neither constant nor exactly equal to the ratio of the pulley diameters. V2<VB<V1
上充通大学 Shanghai Jiao Tong University Flexible Transmission Elements2 Belt Drives >Used where rotational speeds are relatively high >Linear speed of belt about 2,500 to 7,000 ft/min Ideal around 4,000 ft/min. >At lower speeds, Tension in the belt becomes too large for typical belt cross sections >At higher speeds, √Dynamic effects such as centrifugal forces(离心力)， belt whip,vibration reduce effectiveness of drive and its life. 7
7 Flexible Transmission Elements2 •Belt Drives Used where rotational speeds are relatively high Linear speed of belt about 2,500 to 7,000 ft/min Ideal around 4,000 ft/min. At lower speeds, Tension in the belt becomes too large for typical belt cross sections At higher speeds, Dynamic effects such as centrifugal forces(离心力), belt whip, vibration reduce effectiveness of drive and its life
上泽充通大学 Shanghai Jiao Tong University Flexible Transmission Elements2 Chain Drives(链传动) >A chain drive is a flexible power transmission element that operates on a set of toothed wheels called sprockets(链轮) >Used at lower speed where high torques are needed >At higher speeds, Noise,impact between chain link and sprocket teeth and lubrication become major problems. Xooo66o06形
8 Flexible Transmission Elements2 •Chain Drives（链传动） A chain drive is a flexible power transmission element that operates on a set of toothed wheels called sprockets （链轮） Used at lower speed where high torques are needed At higher speeds, Noise, impact between chain link and sprocket teeth and lubrication become major problems
上帝充通大￥ Shanghai Jiao Tong University Advantages of Different Transmissions3 Advantages of Belt Drives(high-speed,low-torque) 1.Electrical insulation provided because there is no metal-to- metal contact between driver and driven units. 2.Less noise than with a chain drive 3.Flat belts can be used for extremely long center distances where chain weight would be excessive 4.Flat belts can be used at extremely high-speeds where chain inertia (must be considered as influencing chain fit at sprocket and chain tension. 5.No lubrication required. 6.Shaft center distance variation and shaft alignment is much less critical than for gear drives or chain drives. 9
9 Advantages of Different Transmissions3 Advantages of Belt Drives(high-speed, low-torque) 1. Electrical insulation provided because there is no metal-tometal contact between driver and driven units. 2. Less noise than with a chain drive 3. Flat belts can be used for extremely long center distances where chain weight would be excessive 4. Flat belts can be used at extremely high-speeds where chain inertia（惯性） must be considered as influencing chain fit at sprocket and chain tension. 5. No lubrication required. 6. Shaft center distance variation and shaft alignment is much less critical than for gear drives or chain drives
上充通大学 Shanghai Jiao Tong University Advantages of Different Transmissions3 Advantages of Chain Drives(low-speed,high-torque) 1.Shaft center distance variation may be more easily accommodated than with gear drives 2. Chains are easier to install and replace than belts because the center distance between driven and driver units need not be reduced for installation(splice and link belts overcome this objection at the cost of lower power ratings). 3. Chains require no tension on the slack side(松边)，so that bearing loads are reduced. 4. Chains do not slip or creep as belt drives do (except toothed belts). 5. Chain drives more compact because sprocket diameters are smaller and chains are narrower than sheaves and belts for same power transfer. 6. Chains do not develop static charges 7. Chains do not deteriorate (with age,heat or oil and grease. 8. Chains can operate at higher temperatures than belts. 10
10 Advantages of Different Transmissions3 Advantages of Chain Drives(low-speed, high-torque) 1. Shaft center distance variation may be more easily accommodated than with gear drives 2. Chains are easier to install and replace than belts because the center distance between driven and driver units need not be reduced for installation (splice and link belts overcome this objection at the cost of lower power ratings). 3. Chains require no tension on the slack side（松边）, so that bearing loads are reduced. 4. Chains do not slip or creep as belt drives do (except toothed belts). 5. Chain drives more compact because sprocket diameters are smaller and chains are narrower than sheaves and belts for same power transfer. 6. Chains do not develop static charges 7. Chains do not deteriorate（老化） with age, heat or oil and grease. 8. Chains can operate at higher temperatures than belts