Mechanical transmission is widely used in mechanical engineering, which mainly refers to the transmission of power and motion through mechanical means.It can be divided into two categories: one is between partsfrictionPower transmittingFriction driveSecond, rely onDriving partsAndFollowerMeshing transmission that transmits power or motion through meshing or with the aid of intermediate piece.
Chinese name
mechanical drive
Foreign name
mechanical drive
Mainly refers to
Mechanical transmission of power and motion transmission
Other
The magazine of the same name Mechanical Transmission
There are many forms of mechanical transmission, which can be mainly divided into two categories: ① transmission of power and motion by friction between partsFriction drive, includingBelt drive、Rope driveandFriction wheel driveEtc.Friction transmission is easy to realizeStepless speed change, most of them can adapt to transmission occasions with large shaft spacing, and overload slipping can also play a buffer and protection roletransmissionHowever, this kind of transmission can not be used in high-power occasions, nor can it guarantee accuratetransmission ratio。②Rely on the driving parts andFollowerMeshing transmission that transmits power or motion by engaging or by means of intermediate piece, includinggear drive、Chain drive、Screw driveandHarmonic driveEtc.Meshing transmission can be used in high-power occasions with accurate transmission ratio, but generally requires high manufacturing accuracy and installation accuracy.
MechanicsTransmission mechanismThe way, direction or speed of motion provided by the power can be changed and used purposefully by people.In ancient China, there were many types of transmission mechanisms, which were widely usedSeismograph、BlowerAnd so on, are the products of mechanical transmission mechanism.Transmission mechanism in ancient China mainly includes gear transmissionRope strapDrive and chain drive.
1、gear drive。It appeared no later than the Western Han DynastyGuide car、Ji Li Drum Car, Eastern Han DynastyZhang HengInvented water powerAstronomical instrumentBoth use quite complicated gearsdrive system 。These gears are only used to transmit motion, and their strength requirements are not high.As for the gear used in production, it is required to transmit greater power, generally greater force, and higher strength requirements.Used in ancient timesanimal power, hydraulic and wind power for water liftinggrain processingSuch gears shall be applied during operation.For example, inRolloverThe primary gear transmission mechanism must be applied to change the direction and transmission of motion and adapt to the working requirements of rollover.
2、Chain drive。It appeared very early in ancient China. There were bronze chains on the harness of the Shang Dynasty, and chains were also used as decorations on other bronze and jade articles.The bronze chariot of the Qin Dynasty unearthed in Xi'an has very exquisite metal chains.But these are not chain drives.As a power transmission chain, it appeared in the Eastern Han Dynasty.Eastern Han DynastyBi LanTake the lead in inventing rollover to divert water.According to its working principle and kinematic relationship, it can be regarded as a chain drive.Up and down of rolloverSprocketOne is active, one is driven, and the flap around the wheel isDrive chain, this drive chain is also used asLifting waterTherefore, rollover is a special case of chain drive.In the Song Dynasty,Su SongManufacturedWater transport instrument stageUp, there is a "sky ladder", which is actually an iron chain. The lower horizontal axis drives the upper horizontal axis through the "sky ladder", thus forming a real chain drive.
mechanical drive
3. Rope belt drive.This is a transmission mode using friction.In the Western Han Dynasty, Sichuan producedWell saltDuring shaft sinking and water lifting, oxen are used to drive the big rope sheave, and the rope on the sheave is wound up to lift the drilling tools, brine, etc.Handshake appeared in the Western Han Dynastyspinning wheel, is a typical rope belt transmission.In the Western Han DynastyRelief stoneUp, there are some hand shakesSpinning wheel diagramIt can be clearly seen that the big rope sheave is driven by the ropespindleRotate the big rope sheave by hand for one circle, and the spindle rotates for dozens of cycles, with high efficiency.The spinning wheels with three spindles and five spindles will be more efficient.Water transportation in Yuan DynastyBig spinning wheelIt is also driven by rope belt.In the Eastern Han Dynasty, metallurgyhandicraft industryThere is an important invention“Water drainage”, forblast。The working principle of the rope belt transmission is: hydraulic horizontalWater wheelRotation, waterwheel axleIt is equipped with a big sheave, which drives the small sheave through the rope belt, and the upper end of the small sheave shaftcrankIt rotates with it and is pushed by connecting rodBlowerAir blast.This waterDrum beatThe wind is very effective, which can be equivalent to hundreds of horses.Its appearance indicates that the developed machinery in the Eastern Han Dynasty has appeared in China, so it is of great significance.
skinBelt driveBelt transmission is a transmission mode with intermediate flexible parts, which is widely used in mechanical transmission, especially in belt transmissionV-belt drive It is widely used.
1、 Type of belt drive
Belt drive[1]
Belt transmission is a kind of transmission mode that uses the belt as an intermediate flexible part to transmit motion or power.
According to different transmission principles, belt transmission is divided into friction type（Flat belt drive, V-belt drive, etc.) and meshing type（Synchronous belt）Two types.
mechanical equipmentThe friction type belt drive is the most common belt drive used in. The following is an example of V-belt drive to introduce the basic knowledge of belt drive.
Drive beltIt is sleeved on the driving pulley 1 and driven pulley 2,Paired bandWhen a certain tension force is applied, the contact surface between the belt and pulley will generatePositive pressure；Driving wheelWhen rotating, the driven wheel is driven to rotate by the friction between the belt and the pulley.
The basic principle of belt transmission is to rely on the friction between belt and pulley to transmit motion and power.
Because of the bandFlexible, and lean againstfrictionIt has simple structure, stable transmission, low noise, shock absorption and overloadTime bandIt will slip on the belt pulley, which will affect other partsoverload protectionFunction, applicable toCenter distanceLarge transmission and other advantages.
However, belt transmission also has many disadvantages, mainly including: it cannot guarantee accurate transmission ratio,transmission efficiency Low (about 0.90~0.94), short service life of the belt, not suitable for use in high temperature, flammable, oil and water situations.
2. Transmission ratio of belt drive
In the belt drive, the driving wheel speed andDriven wheelThe speed ratio is called the transmission ratio and is represented by symbols.
4、 Common belt drive
There are two common types of belt transmission, namely flat belt transmission and V-belt transmission.
1. Flat belt drive
Cross sectionIt is a flat rectangle, and the working is circularInternal surfaceAnd pulleyOuter surfaceContact.Flat beltThe transmission structure is simple, the flat belt is thin, and the flexibility and torsion are good, so it is suitable for high-speed transmission andCross driveOr interlacedHalf cross drive
2. V-belt drive
The cross section isIsosceles trapezoid, placed in the pulley groove during operation, on both sidesFace contactThe friction force is large and the transmission capacity is strong.
When the belt drive is working, the center distance between the two pulleys should be adjustable to make the belt obtain the required tension;The belt will inevitably producePlastic deformationAnd appearedRelaxation phenomenon, reducing its transmission capacity, so generally belt transmission should be equipped with tensioning device.The tensioning methods of belt drive mainly include adjusting the center distance and usingTensionerThere are two types, of which there are regular tensioning and automatic tensioning respectively.
6、 Installation and maintenance
To improveV-beltThe installation, repair and maintenance of the belt transmission device must be properly done to ensure the efficiency of the transmission, extend the service life of the V-belt and ensure the normal operation of the belt transmission.
1. The V-belt must be correctly installed in the groove, and the outer edge of the belt is generally flush with the rim.
2. In the V-belt drive, the axes of the two pulleys should be parallel, and the corresponding V-groove of the two pulleysSymmetry planeIt shall coincide.
3. When disassembling and installing the V-belt, the center distance between the two pulleys should be reduced first to avoid damaging the V-belt or equipment by hard prying.After the belt is covered, adjust the center distance back to the correct position, and the belt should be moderately tight.
4. V-belt drive must be installedprotection cover, to prevent lubricating oilcutting fluidOr other sundries splashed onto the V-belt to affect the transmission and prevent personal injury accidents.
5. For a group of V-belts, it is generally necessary toGroupReplace the old belt and the new belt cannot be mixed.
gear drive
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gear drive
gear driveIt is composed of twogearThey are meshed with each other.Gear transmission is one of the most widely used transmission forms.
1. The range of power and speed transmitted by gears is large, ranging from very small to hundreds of thousands of kilowatts,Circumferential velocityIt can range from very small to more than 100 meters per second.The gear size can range from less than 1mm to more than 10m.
2. Gear transmission belongs to meshing transmissiontooth profileIt is a specific curve, the instantaneous transmission ratio is constant, and the transmission is stable and reliable.
3. The gear transmission efficiency is high and the service life is long.
4. There are many kinds of gears, which can meet the needs of various transmission forms.
5. The manufacturing and installation accuracy of gears are required to be high.
2、 Classification of gear transmission
There are many kinds of gears, which can be classified in different ways.
According to the meshing mode, gear transmission includes external meshing transmission and internal meshing transmission.
By gearTooth orientationDifferent points, gear transmission has straight teethcylindrical gearTransmission;Helical toothCylindrical gear drive；Herringbone cylindrical gear transmission and straight bevel gear transmission.
3、 Standard straight cylindrical gear drive
Spur gear transmission is the most basic form of gear transmission, which is widely used in mechanical transmission devices.
stayEnd planeYes, yesEnd profileThe radial line at the intersection of the reference circle and the tooth profile at this pointtangentThe acute angle is called tooth angle.
gear drive
Standard provisionsinvolute gear The standard tooth profile angle of is a=20 °.（3）modulusm
PitchThe quotient obtained by dividing p by pi is called modulus, which is in mm and has been standardized.
4、 Other types of gear transmission
In addition to straight cylindrical gear transmission, there are helical cylindrical gear transmission, straight bevel gear transmission andworm driveEtc.
1. Helical cylindrical gear drive
Tooth line ishelical lineThe cylindrical gear of is called helical cylindrical gear.
Helical cylindrical gear according toHelix angleThere are two kinds of gears: left hand gear and right hand gear. The rotation direction can be usedRight hand ruleTo judge.Reach out your right hand, palm up, four fingers pointingGear shaftDirection: if the tooth direction is the same as the thumb direction, it is right-handed; otherwise, it is left-handed.
When a pair of helical cylindrical gears mesh, because the gear teeth are helically placed on the cylindrical surface, the two meshing gear teethtooth surfaceWhen a pair of spur gears is engaged, the two meshing tooth surfaces are in contact with each other along the full length of the tooth direction at the same time, and then disengage at the same time.Therefore, helical cylindrical gear transmission has good stability and small impact, especially under high speed and heavy load.
Helical cylindrical gear transmission is suitable for transmission between two parallel shafts with high transmission stability requirements.
Bevel gear driveIt is used for transmission between two intersecting axes in space. Generally, it is used when two axes intersect 90 ° vertically.
5、 Gear failureform
Gear onworking processThe phenomenon that it is damaged for some reason and loses its normal working ability is called failure.There are many failure forms of gears, and the common failure forms are:
1. Tooth surface wear
In the process of gear transmission, there is relative sliding between the meshing surfaces of gear teeth.When the gear is under force, the relative sliding between the tooth surfaces makes the tooth surfaces wear.Wear will damage the tooth surface shape, resulting in unstable transmission;In addition, wear makes the gear teeth thin, resulting inBacklashThe strength of gear teeth decreases with the increase.Gear surface wear is caused by poor lubrication conditionsOpen gear drive(Exposed gear transmission), which is also open typeworm driveThe main failure mode of.
2. Broken gear teeth
When the gear is working, the force on its teeth is equivalent tocantilever beam, at the tooth rootbending momentMaximumStress concentration。During meshing, the bending moment at the root of the gear changes alternately, so it is most likely to occur therefatigue crack The failure form of gear teeth is called fatigue fracture of gear teeth.Another kind of gear breaking is long-term overload or excessiveImpact loadThe sudden breaking of is called overload breaking.
At low speed and heavy loadWorking conditionsThe tooth surface of the gear bears great pressure andfrictionBecause of these forces, the local tooth surface of the gear with soft material may producePlastic flowWhich makes the tooth surface have grooves or bulgesPrismatic platformThus destroying the tooth profile of the gear and making the gear lose its working ability.This failure form of gear is called plastic deformation of gear teeth.
4. Tooth surface pitting
When the gear is working, when the meshing surface is repeatedly subjected to contact extrusion, and the resulting pressure is too large or the use time is too long, the tooth surface will produce slight fatigue cracks.With the continuous operation of the gear, the cracks will expand along the surface layer, causing small pieces of metal to peel off on the tooth surface, formingPockmarksAnd pits.This failure form of gear tooth surface is called tooth surface pitting.Serious pitting corrosion on the tooth surface will damage the working surface of the gear teeth, resulting in unstable transmission, noise, and even loss of working ability of the gear.
Tooth surface pitting is a kind of failure mode that usually occurs in well lubricatedClosed gear driveMedium.
In high speed and heavy load closed gear transmission, it is difficult to lubricate the tooth surface. Under the action of heavy load, local high temperature will be generated on the meshing surface to make it stick together. When the gear continues to move, part of it will be torn off on the softer tooth surfaceMetallic materialsThe failure caused by bonding and tearing of tooth surface is called tooth surface gluing.After the tooth surface is gluedSevere damageGear failure caused by tooth surface.This kind of failure is very easy to occur in closed worm drive.
Chain drive
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Chain drive
The chain drive is composed of two gears with special tooth shape and a closed chainDriving sprocketOf the chainChain linkThe meshing drives the driven sprocket which meshes with the chain to drive.The chain drive is mainly used in places where the transmission ratio is required to be more accurate, the two shafts are far apart, and gears are not suitable.This is our common bicycle sprocket chain transmission principle.
In mechanical transmission, the commonly used transmission chain isRoller chain(also called sleeve roller chain).Roller chain consists of inner chain plate 1Outer chain plate2、pin shaft3. The sleeve 4 and the roller 5 are composed.
Roller chainInner chain plateUsed separately with sleeve, outer chain plate and pin shaftInterference fitFixed, between pin shaft and sleeve, roller and sleeveClearance fit；Each chain link can be freely bent and extended, and the roller and sleeve can rotate relatively.When the roller chain is meshed with the sprocket, the sleeve and the sprocket tooth are meshed by the rollerdirect contact Ofsliding frictionConvert toRolling frictionSo as to reduce the wear of sprocket teeth.
The length of roller chain is expressed by the number of nodes.In order to make both ends of the chain easy to connect, the number of chain links should be even as far as possiblecotter pinOr spring clip locking.When the number of links is odd, the link head needs to useTransition linkThe transition link is not only complex to manufacture, but also has low transmission capacity, so it should be avoided as far as possible.
2. Marking of roller chains
Roller chains are standard parts, which are marked as:
Chain number - row number - number of chain linksStandard No
Tag example
08A—1—88GB/T1243-1997 refers to roller chain with chain number of 08A (pitch of 12.70mm), single row and 88 knots.
3. Use of chain drive
(1) To ensure the normal operation of the chain drive, the axes of the two sprockets should be parallel to each other, and the two sprockets should be located in the same vertical plane.
(2) In order to improve the quality and service life of chain drive, attention should be paid to lubrication.
(3) Chain drive can not be appliedPreloadIf necessary, the tensioner can be used.
(4) For safety and dust prevention, the chain drive shall be equipped with a protective cover.
worm drive
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worm drive
When a gear has one or moreHelical tooth, and similar to the turbine (similar toHelical gear）Meshing to form interlacingShaft driveThis transmission is calledwormDrive.Worm gearTransmission is used when two shafts intersect at 90 degrees, but they are neither parallel nor intersected with each otherWorm gearDuring transmission, the worm isDriving partsThe worm gear is a passive part.
(1) Features of worm drive
Single stage transmission can achieve a large transmission ratio, compact structure, smooth transmission, no noise, but low transmission efficiency.
(2) Judgment of Turbine Steering in Worm Drive
The relationship between worm and turbine steering in worm drive depends on therelative position, worm rotation direction and its rotation direction.
The left hand orRight hand rule, when the worm is right-handed (the worm is also left-handed and right-handed, and the judgment method ishelical gearThe direction judgment method is the same), the right hand rule is used, and the worm is left handedLeft-handed rule。Bend four fingers to point to the rotation direction of the worm (the straight arrow indicates the circumference of the visible side of the wormDirection of movement）, the opposite direction of thumb is the direction of motion of the turbine relative to the worm.
(1) BiographyForce spiral: It mainly transmits power and requires a smaller torque to produce a largeraxialThrust, for overcomingWorking resistance。Such as the screw of various lifting or pressurizing devices.This kind of force transmission screw mainly bears a lot ofaxial force, generally abbreviated, every timeworking hoursIt is short and its working speed is not high.
(2) Conduction spiral: It mainly transmits movement, and sometimes bears large axial load.Such as machine toolFeed mechanismSpiral, etc.The conduction screw mainly works continuously for a long time and has a high working speed. Therefore, it is required to have a highTransmission accuracy。
(3) Adjust Spiral: to adjust and fix the relative position of parts.Such as the screw of fine adjustment mechanism in machine tools, instruments and test devices.The adjusting screw does not rotate frequently, usuallyNo loadLower adjustment.
Features of spiral transmission: high transmission precision, smooth operation, no noise, easy self-locking, and large power transmission.
importance
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Working machineIt usually dependsPrime moverProvide a certain form of energy, but put the prime mover and working machineDirect connectionThe situation is rare, and it is often necessary to add power transmission or change between the twomotion state Drive of:
(1) The speed required by the working machine is generally inconsistent with the optimal speed of the prime mover.
(2) Many working machines need speed adjustment according to production requirements, but it is uneconomical and impossible to achieve this goal by relying on the speed of the prime mover.
(3) In some cases, a prime mover is required to drive several working machines with different working speeds.
(4) For safety and easy maintenance, or because of theOverall dimensionDue to restrictions and other reasons, the prime mover and the working machine cannot be directly connected together.
Design outline
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When designing transmission, if transmission power, transmission ratio and working conditions have been determined, different types of transmission have their own advantages and disadvantages.
(1) Power and efficiency
The power transmitted by various transmissions depends on their transmission principlescarrying capacity, load distribution, working speed, manufacturing accuracyMechanical efficiency、feverConditions and other factors.
Efficiency is one of the main indexes for evaluating transmission performance.
(2) Speed
Speed is the main driving forceKinematic characteristicsone of.Improving transmission speed is an important development direction of machines.
(3) Overall dimension, quality, cost
The overall dimensions and quality of transmission are closely related to the power and speed, as well as transmission partsMechanical properties of materialsof
Transmission ratio is one of the kinematic characteristics of transmission.
