上海交通大学：《Design & Manufacturing II and Project》课程教学资源（讲义）Lecture 9 Transmission Gears

ME350 Mechanical Design and Manufacturing ll ME350 Power/Energy Transmission Ill: Gears 1

ME 350 1 ME 350 Mechanical Design and Manufacturing II Power/Energy Transmission III: Gears

Lectures ME350- Power/Energy Conversion (Electrical Motors) Power/Energy Transmission (Gears, Belt Drives, Power Screwsy Joints Transmission (Fasteners, Support Connectors) (Bearings) Structural Support (Frames) Tools Statics,Dynamics, Stress Analysis,etc.. 2

ME 350 2 Lectures Power/Energy Conversion (Electrical Motors) Power/Energy Transmission (Gears, Belt Drives, Power Screws) Power/Energy Transmission (Gears, Belt Drives, Power Screws) Transmission Support (Bearings) Joints (Fasteners, Connectors) Structural Support (Frames) Tools Statics, Dynamics, Stress Analysis, etc

Transmission Elements2 ME350 Gear Drives >Gears change rotational velocity and torque to suit motor and load conditions. >Can be used to simply transport power from one shaft to another. >Highly efficient with output power approximately equal to input power. V-belt drive Chain drive Driven machine (a)Sketch of combination drive th)Photograph of an actual drive installation.Note that from the belt

ME 350 3 Transmission Elements 2 Gear Drives ¾Gears change rotational velocity and torque to suit motor and load conditions. ¾Can be used to simply transport power from one shaft to another. ¾Highly efficient with output power approximately equal to input power

Transmission Elements2 ME350- Belt Drives >Used where rotational speeds are relatively high. >At lower speeds,tension in belt becomes too large for typical belt cross sections >At higher speeds,dynamic effects such as centrifugal forces,belt whip,and vibration reduce effectiveness of drive and its life. Chain Drives >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. 4

ME 350 4 Transmission Elements 2 Belt Drives ¾Used where rotational speeds are relatively high. ¾At lower speeds, tension in belt becomes too large for typical belt cross sections ¾At higher speeds, dynamic effects such as centrifugal forces, belt whip, and vibration reduce effectiveness of drive and its life. Chain Drives ¾Used at lower speed where high torques are needed. ¾At higher speeds, noise, impact between chain link and sprocket teeth and lubrication become major problems

Advantages of Different Transmissions4 ME350 Advantages of Belt Drives >Electrical insulation is provided because there is no metal- to-metal contact between driver and driven units. There is less noise than with a chain drive >Flat belts can be used for extremely long center distances where chain weight would be excessive Flat bets can be used at extremely high-speeds where chain inertia must be considered as influencing chain fit at the sprocket and chain tension. No lubrication is required. >Shaft center distance variation and shaft alignment is much less critical than for gear drives or chain drives. 5

ME 350 5 Advantages of Different Transmissions 4 Advantages of Belt Drives ¾ Electrical insulation is provided because there is no metal￾to-metal contact between driver and driven units. ¾ There is less noise than with a chain drive ¾ Flat belts can be used for extremely long center distances where chain weight would be excessive ¾ Flat bets can be used at extremely high-speeds where chain inertia must be considered as influencing chain fit at the sprocket and chain tension. ¾ No lubrication is required. ¾ Shaft center distance variation and shaft alignment is much less critical than for gear drives or chain drives

Advantages of Different Transmissions ME350 Advantages of Chain Drives Shaft center distance variation may be more easily accommodated than with gear drives ● 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). Require no tension on slack side,so bearing loads are reduced. Do not slip or creep as do belt drives (except for toothed belts). Chain drives are more compact because sprocket diameters are smaller and chains are narrower than sheaves and belts for the same power transfer. Chains do not develop static charges Chains do not deteriorate with age,heat or oil and grease. Chains can operate at higher temperatures than belts. 6

ME 350 6 Advantages of Different Transmissions 4 Advantages of Chain Drives • Shaft center distance variation may be more easily accommodated than with gear drives • 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). • Require no tension on slack side, so bearing loads are reduced. • Do not slip or creep as do belt drives (except for toothed belts). • Chain drives are more compact because sprocket diameters are smaller and chains are narrower than sheaves and belts for the same power transfer. • Chains do not develop static charges • Chains do not deteriorate with age, heat or oil and grease. • Chains can operate at higher temperatures than belts

Advantages of Different Transmissions ME350- Advantages of Gear Drives Gear drives are more compact than chain or belt drives because center distances are minimum. Gears have greater speed capabilities than either belts or chains. Gears have a greater range of speed ratios than chains. Gears can better transfer high power at high speed than can either belts or chains. Metal gears do not deteriorate with age,heat or oil and grease and they do not develop static electric charges. 7

ME 350 7 Advantages of Different Transmissions 4 Advantages of Gear Drives • Gear drives are more compact than chain or belt drives because center distances are minimum. • Gears have greater speed capabilities than either belts or chains. • Gears have a greater range of speed ratios than chains. • Gears can better transfer high power at high speed than can either belts or chains. • Metal gears do not deteriorate with age, heat or oil and grease and they do not develop static electric charges

Gears4 ME350- (a) (b) (c) () (d) (e) Figure 13.0.1(a)Spur gear.(b)worm gear.(c)helical gear,(d)rack,(e)internal gear,and(f)straight 8 bevel gear.Source:Boston Gear,Quincy,MA

ME 350 8 Gears 4

Basic Gear Types5 ME350 .There are four main types of gears: >Spur Gears Helical Gears Bevel Gears >Worm Gears 9

ME 350 9 Basic Gear Types 5 •There are four main types of gears: ¾Spur Gears ¾Helical Gears ¾Bevel Gears ¾Worm Gears

Basic Gear Types -Spur Gears ME350— These gears have teeth parallel to the axis of rotation and are used to transmit motion and power from one shaft to another parallel shaft. 10

ME 350 10 Basic Gear Types – Spur Gears These gears have teeth parallel to the axis of rotation and are used to transmit motion and power from one shaft to another parallel shaft