Transmission mechanism is a component or mechanism that transfers power from one part of the machine to another to make the machine or machine parts move or run.
(1) Change the output torque of the power machine to meet the requirements of the working machine;
(2) Change the movement output by the power machine into the form required by the working machine, such as changing the rotary movement into linear movement, or vice versa;
(3) Transfer the mechanical energy of one power machine to several working machines, or transfer the mechanical energy of several power machines to one working machine;
(4) For other special functions, such as facilitating the control, assembly, installation, maintenance and safety of the machine, the transmission device is set.
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According to different working principles, transmission modes can be divided into:
mechanical drive
It refers to the transmission of power and motion through mechanical means.It can be divided into two categories: one is the transmission of power and friction transmission by friction between parts, and the other is the transmission of power or motion by meshing of driving parts and driven parts or by means of intermediate parts.
Fluid transmission
It refers to a transmission using fluid as working medium.It depends on the static pressure of the liquid to transfer energyHydraulic transmission。Hydraulic transmission refers to the transmission of energy by the hydrodynamic action between the impeller and the liquid.The transmission of energy by the pressure of gas is called pneumatic transmission.
electric drive
Means to useMotorIt converts electric energy into mechanical energy to drive various types of production machinery, traffic vehicles and the transmission that needs movement in life, also known as electric drive.
Compound transmission
It refers to the mechanism or structure using two or more transmission modes.
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Gear transmission mechanism
Gear transmission is a kind of meshing transmission, which can be divided into gear units with two parallel shafts and gear units with two non parallel shafts.
(2) Applicable to a wide range of loads and speeds.
(3) High efficiency, long service life, compact structure, small external size;
(4) It can transfer the movement between two axes arbitrarily configured in space.
Main disadvantages:
(1) Compared with spiral drive and belt drive, the vibration and noise are large, and the stepless speed regulation is not allowed;
(2) The distance between transmission shafts shall not be too large;
(3) Complex processing and high manufacturing cost.
Classification of gear trains: fixed axle gear trains, epicyclic gear trains.When the fixed shaft gear train rotates, the position of each gear axis is fixed.When the epicyclic gear train is running, the geometric axis of at least one gear is the gear train that rotates around the geometric axis of the other gear.The epicyclic gear train is also divided into differential gear train and planetary gear train.The differential gear train means that both center wheels rotate.The planetary gear train is a fixed center wheel.The hybrid gear train has both fixed axle gear train and epicyclic gear train.
Function of gear train:
(1) Large transmission ratio can be achieved;
(2) Two shaft transmission can be realized at a distance;
(3) The driven shaft can obtain several different transmission ratios;
(4) Different steering directions of driven shaft can be obtained by changing the number of gears;
Fig. 1 Gear Transmission
(5) Realize the synthesis and decomposition of motion.
Chain drive mechanism
Fig. 2 Chain Drive
Chain drive is mainly composed of driving sprocket, driven sprocket and chain, as shown in Figure 2.
Transmission ratio: i=n2/n1=z1/z2.
According to the above formula, the transmission ratio of chain drive is inversely proportional to the number of sprocket teeth.
advantage:
(1) Compared with belt transmission, the average transmission ratio is accurate, the transmission power is large, and the contour size is small.
(2) Compared with gear transmission, the transmission center distance is large.
(3) Able to work under low speed, heavy load and high temperature conditions.
(4) High efficiency, up to 0.99.
Disadvantages:
(1) Unable to maintain constant instantaneous transmission ratio;
(2) The chain unit length and weight are large, causing noise.The rapid reverse performance is poor and cannot be used for high speed.
Belt transmission mechanism
Fig. 3 Belt drive
Belt drive is to transfer movement and force by friction between belt and pulley, as shown in Figure 3.
The belt used in the belt transmission mechanism can be divided into flat belt, V-belt, round belt and toothed belt.
Flat belt transmission consists of open transmission, cross transmission and semi cross transmission.
Transmission ratio: i=n2/n1=d1/d2
Belt drive features:
(1) Stable movement without noise, which can cushion impact and absorb vibration;
(2) Simple structure, long transmission distance;
(3) Simple manufacturing and installation, convenient maintenance, no lubrication;
(4) Overload slipping can protect;
(5) Large external size, low efficiency, short service life and low transmission accuracy.
Worm gear and worm drive mechanism
Fig. 4 Worm gear and worm drive
Worm gear and worm mechanism is often used to transmit the motion and power between two staggered shafts.Worm gear and worm are equivalent to gear and rack in the middle plane, and the worm is similar to the screw in shape, as shown in Figure 4.
Worm gear and worm drive features:
(1) It can obtain a large transmission ratio, which is more compact than the staggered helical gear mechanism;
(2) The two meshing tooth surfaces are in line contact, and the bearing capacity is much higher than that of the staggered helical gear mechanism;
(3) Worm transmission is equivalent to spiral transmission, which is multi tooth meshing transmission, so the transmission is stable and the noise is very low;
(4) It is self-locking.When the lead angle of the worm is less than the equivalent friction angle between the meshing gear teeth, the mechanism is self-locking and can achieve reverse self-locking, that is, only the worm can drive the worm, but not the worm.For example, the reverse self-locking of the self-locking worm mechanism used in lifting machinery can play a role in safety protection;
(5) Low transmission efficiency and serious wear.When worm gear and worm are engaged, the relative sliding speed between the meshing gear teeth is large, so the friction loss is large and the efficiency is low.On the other hand, the relative sliding speed causes serious wear and heat on the tooth surface. In order to dissipate heat and reduce wear, more expensive materials with good friction and wear resistance and good lubrication devices are often used, so the cost is high;
(6) The axial force of worm is large.
Cam mechanism
The cam mechanism converts the continuous rotation of the cam into the reciprocating movement or swing of the follower, as shown in Figure 5.
Features: simple and compact mechanism;It is easy to wear, and is mainly used for control mechanism and regulating mechanism with little power transmission.[1]
