圈上海夫通大华 e寸B口 LECTURE 10 ME371/ME337 DESIGN AND MANUFACTURING Belt Drives Covered: Ch17 in Mechanical Engineering Design SHAN 圈上泽夫通大学 Lectures Power/Energy Conversion (Electrical Motors) Power/Energy Transmission (Gears,Cam,Linkage, Belt Drives, Power Screws Transmission Joints (Fasteners, Support Connectors) (Bearings) Structural Support (Frames) Tools Statics,Dynamics, Stress Analysis,etc. 1
1 Belt Drives LECTURE 10 ME371/ME337 DESIGN AND MANUFACTURING Covered: Ch17 in Mechanical Engineering Design Lectures Power/Energy Conversion (Electrical Motors) Transmission Support (Bearings) Joints (Fasteners, Connectors) Structural Support (Frames) Tools Statics, Dynamics, Stress Analysis, etc. Power/Energy Transmission (Gears, Cam, Linkage, Belt Drives, Power Screws)
国上海支大华 Outline Belt drive system introduction Belt drive system analysis Belt drive system design 圆上清支大华 Applications 2
2 Outline Belt drive system introduction Belt drive system analysis Belt drive system design Applications
Timing-Belt Drive 桑塔纳轿车(2000)发动机 V-Belt Drive 手扶拖拉机驱动装置 3
3 Timing-Belt Drive V-Belt Drive
Poly-rib Belt 北京”切诺基”吉普车发动机 Flat Belt Drive 大理石切害割机(125kW) 4
4 Poly-rib Belt Flat Belt Drive
圈上海文通大华 Basic Belt Drives A belt drive is a flexible power transmission element that seats tightly on a set of pulleys(带轮sheave) ▣ When used for speed reduction,the smaller sheave is mounted on the high-speed shaft,e.g.shaft of an electric motor.Larger sheave is mounted on driven machine. Belt is installed by placing it around the two sheaves while center distance between them is reduced.Then the sheaves are moved apart placing the belt in high initial tension(初拉力). © 上海充廷大学 Belt Type 口 Four principal types of belts:Crowned pulleys are used for flat belts,and grooved pulleys,or sheaves,for round and V belts.Timing belts require toothed wheels,or sprockets. Belt Type Figure Joint Size Range Center Distance Yes 0.031o0.20im No upper limit I= 10.75to5mm Round 0立 Yes d=文o是in No upper limit ☑ None b=/0.31tor 18to19 Timing y None p =2 mm and 5
5 Basic Belt Drives A belt drive is a flexible power transmission element that seats tightly on a set of pulleys（带轮 sheave） When used for speed reduction, the smaller sheave is mounted on the high-speed shaft , e.g. shaft of an electric motor . Larger sheave is mounted on driven machine. Belt is installed by placing it around the two sheaves while center distance between them is reduced. Then the sheaves are moved apart placing the belt in high initial tension（初拉力）. Four principal types of belts: Crowned pulleys are used for flat belts, and grooved pulleys, or sheaves, for round and V belts. Timing belts require toothed wheels, or sprockets. Belt Type
圈上泽支大峰 Flat or Round Belt Simplest type Often made from leather or rubber-coated fabric. Crowned pulleys are used for flat belts,and grooved sheaves for round belts. Driving force is limited by pure friction between belt and sheave. Some designers prefer flat belts for delicate machinery because belt will slip if torque tends to rise to a level high enough to damage the machine. 布平带 物边平帝 圈上泽夫道大学 V-Belt V-shape causes belt to wedge tightly into groove to increases friction and allows high torques to be transmitted before slipping occurs. Most belts have high-strength cords positioned at pitch diameter of belt cross section to increase tensile strength Cords made from natural fibers,synthetic strands or steel Embedded in firm rubber compound to provide flexibility needed to allow belt to pass around sheave. Often outer fabric cover is added to give belt good durability. 包布y 勿题V州 6
6 Flat or Round Belt Simplest type Often made from leather or rubber-coated fabric. Crowned pulleys are used for flat belts, and grooved sheaves for round belts. Driving force is limited by pure friction between belt and sheave. Some designers prefer flat belts for delicate machinery because belt will slip if torque tends to rise to a level high enough to damage the machine. V-shape causes belt to wedge tightly into groove to increases friction and allows high torques to be transmitted before slipping occurs. Most belts have high-strength cords positioned at pitch diameter of belt cross section to increase tensile strength Cords made from natural fibers, synthetic strands or steel Embedded in firm rubber compound to provide flexibility needed to allow belt to pass around sheave. Often outer fabric cover is added to give belt good durability. V-Belt
圈上海文大华 V-Belt Example of V-Belt Construction 普通V带 齿性V带 同步带 年◆单 受 m b)Die cut.cog Timing belt )Wrapped constru Double angle V-bel id)Poly-rib bel e,Vee-band联组V带 双面V带 Dayton,Ohio) 圈上泽夫道大学 Grooved or Timing Belt Requires toothed wheels,or sprockets.Sheaves have mating grooves into which the cogs on belts seat. Can transmit the high forces at low speeds,compete with chain drives. Limited only by tensile strength of belt and shear strength of cogs. 7
7 Example of V-Belt Construction 双面V带 齿性V带 多楔带 同步带 联组V带 普通V带 V-Belt Requires toothed wheels, or sprockets. Sheaves have mating grooves into which the cogs on belts seat. Can transmit the high forces at low speeds, compete with chain drives. Limited only by tensile strength of belt and shear strength of cogs. Grooved or Timing Belt
圆上活支大学 Types of Pulleys and Sheaves Crowned pulleys(Table17-3,5) ·Used for flat belts Grooved Pulleys or Sheaves Used for round or V-belts Toothed wheels or Sprockets Required for timing belts. Dus de ca-eret itcnc a-e:s ey groove 圆上泽夫通大学 Types of Pulleys and Sheaves ▣ Variable Pitch Sheaves Used to change the speed ratio. >As tension increases,spring loaded side of flange moves outward.this causes: Pitch diameter to decrease Speed ratio to reduce. 8
8 Crowned pulleys (Table17-3,5) • Used for flat belts Grooved Pulleys or Sheaves • Used for round or V-belts. Toothed wheels or Sprockets • Required for timing belts. Types of Pulleys and Sheaves Table 17-5 Variable Pitch Sheaves Used to change the speed ratio. As tension increases, spring loaded side of flange moves outward . this causes : • Pitch diameter to decrease • Speed ratio to reduce. Types of Pulleys and Sheaves
圈上海文通大华 Belt Drive Characteristics They may be used for long center distances. Except for timing belts,there is some slip and creep,and so the angular-velocity ratio between the driving and driven shafts is neither constant nor exactly equal to the ratio of the pulley diameters. In some cases an idler or tension pulley can be used to avoid adjustments in center distance that are ordinarily necessitated by age or the installation of new belts. 圈上泽夫通大学 Belt Drive Characteristics 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)，belt whip,vibration reduce effectiveness of drive and its life. 9
9 They may be used for long center distances. Except for timing belts, there is some slip and creep, and so the angular-velocity ratio between the driving and driven shafts is neither constant nor exactly equal to the ratio of the pulley diameters. In some cases an idler or tension pulley can be used to avoid adjustments in center distance that are ordinarily necessitated by age or the installation of new belts. Belt Drive Characteristics 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. Belt Drive Characteristics
圈上海文通大华 Transmissions Advantages ▣ Electrical insulation provided because there is no metal- to-metal contact between driver and driven units. Flat belts can be used for extremely long center distances where chain weight would be excessive No lubrication required. Shaft center distance variation and shaft alignment is much less critical than for gear drives. © 上海充廷大学 Belt Standards ▣ Different organizations have established different standards for belts: >RMA-MPTA-RAC Standard Developed by the Rubber Manufacturers Association,the Mechanical Power Transmission Association,and the Rubber Association of Canada. >ASAE Standards Developed by the American Society of Agricultural Engineers. >SAE Standards Developed by the Society of Automotive Engineers.The standard codes are as follows: SAE Standard J636c:V-belts and pulleys SAE Standard J637b:Automotive V-belt drives SAE Standard J1278:SI synchronous belts and pulleys SAE Standard J1313:Automotive synchronous belt drives SAE Standard J1459:V-ribbed belts and pulleys 40人 Standard V-Belt Sections 10
10 Electrical insulation provided because there is no metalto-metal contact between driver and driven units. Flat belts can be used for extremely long center distances where chain weight would be excessive No lubrication required. Shaft center distance variation and shaft alignment is much less critical than for gear drives. Transmissions Advantages Belt Standards Different organizations have established different standards for belts: RMA-MPTA-RAC Standard Developed by the Rubber Manufacturers Association, the Mechanical Power Transmission Association, and the Rubber Association of Canada. ASAE Standards Developed by the American Society of Agricultural Engineers. SAE Standards Developed by the Society of Automotive Engineers. The standard codes are as follows: • SAE Standard J636c:V-belts and pulleys • SAE Standard J637b:Automotive V-belt drives • SAE Standard J1278:SI synchronous belts and pulleys • SAE Standard J1313:Automotive synchronous belt drives • SAE Standard J1459:V-ribbed belts and pulleys Standard V-Belt Sections