A gear train with a cycloid as a tooth profile. The contact between the tooth surfaces of the transmission is small, the wear resistance is good, and there is no root cutting phenomenon, but the manufacturing precision is high, and the center distance error is very sensitive. Used only in watches and meters.
Characteristics
Gear transmission is a mechanical transmission that utilizes the teeth of the two gears to mesh with each other to transmit power and motion. According to the relative position of the gear axis, it is divided into parallel shaft spur gear transmission, intersecting shaft bevel gear transmission and staggered shaft helical gear transmission. It has the characteristics of compact structure, high efficiency and long life.
Gear transmission refers to the direct transmission of motion and power by the main and driven wheel teeth.
Among all mechanical transmissions, gear transmissions are the most widely used and can be used to transmit motion and power between two axes that are not far from each other.
The characteristics of the gear transmission are: stable gear transmission, accurate transmission ratio, reliable operation, high efficiency, long service life, and large range of power, speed and size. For example, the transmission power can be as small as several hundred thousand kilowatts; the speed can be up to 300m/s; the gear diameter can range from a few millimeters to more than twenty meters. However, the manufacture of gears requires special equipment, and the meshing drive produces noise.
Types of
gear drive
(1) According to the relative position of the two axes and the direction of the teeth, it can be divided into the following types:
Spur gear transmission;
Helical gear transmission
Herringbone gear transmission;
Bevel gear transmission;
Interlaced helical gear drive.
(2) According to the working conditions of the gear, it can be divided into:
Open gear-driven gear transmission with gears exposed and does not guarantee good lubrication.
Semi-open gear transmission, the gear is immersed in the oil pool, with a shield, but not closed.
Closed gear transmission, gears, shafts and bearings are all installed in the closed box, the lubrication conditions are good, the sand is not easy to enter, and the installation is accurate.
Gear transmission has good working conditions and is the most widely used gear transmission.
Design Guidelines Gear Drives For the five failure modes of gears, the corresponding design criteria should be established separately. However, for the tooth surface wear, plastic deformation, etc., since the calculation methods and design data that are widely used in engineering and are effective have not been established, the current design of the gear transmission is usually only to ensure the tooth root bending fatigue strength and to ensure the tooth surface. The two criteria of contact fatigue strength are calculated. For high-speed and high-power gear transmission (such as aero-engine main drive, turbo generator set transmission, etc.), it is also calculated according to the criteria for ensuring the anti-adhesive ability of the tooth surface (refer to GB6413-1986). As for the ability to resist other failures, although the calculations are generally not performed, measures should be taken to enhance the ability of the teeth to resist these failures.
1. Closed gear transmission is known from practice. In closed gear transmission, the contact fatigue strength of the tooth surface is usually guaranteed. However, gears with high tooth surface hardness and low core strength (such as gears with 20 or 20Cr steel after carburizing and quenching) or brittle gears are usually used to ensure the root bending fatigue strength. If both gears are hard toothed and the tooth surface hardness is as high, it depends on the specific situation. Large-capacity transmissions, such as closed-gear transmissions with input power exceeding 75 kW, generate a large amount of heat, which is prone to poor lubrication and gear-to-gluing damage. In order to control the temperature rise, the heat dissipation capacity should also be calculated.
2, open gear transmission gear transmission open type (semi-open type) gear transmission, according to the principle of ensuring the tooth surface anti-wear and root fracture resistance, but as mentioned above, the tooth surface anti-wear ability The calculation method has not been perfected so far, so the split type (semi-open type) gear transmission is currently only designed to ensure the root bending fatigue strength. In order to extend the life of the open (semi-open) gear transmission, the modulus determined can be appropriately increased depending on the specific needs.
As mentioned above, the dimensions of the rims, spokes, hubs, etc. of the gears are usually only for structural design, and no strength calculation is performed.
Gear drive type
Cylindrical gear transmission
Gear transmission is used for transmission between parallel shafts. The general transmission ratio can be up to 8, single 20, two to 45, maximum 60, three to 200, and maximum 300. The transmission power can reach 100,000 kilowatts, the speed can reach 100,000 rpm, and the peripheral speed can reach 300 meters/second. The single stage efficiency is 0.96 to 0.99. The spur gear drive is suitable for medium and low speed drives. The helical gear drive runs smoothly and is suitable for medium and high speed transmission. The herringbone gear drive is suitable for transmissions that transmit high power and high torque. There are three kinds of meshing gears: external gear transmission, which is engaged by two external gears, and the steering of the two wheels is reversed. The internal gear transmission is engaged by an internal gear and a small external gear. The steering is the same; the rack and pinion drive can change the rotation of the gear into a linear movement of the rack, or vice versa.
2. Bevel gear transmission
Used for transmission between intersecting shafts. The single-stage transmission ratio can be up to 6, up to 8, and the transmission efficiency is generally 0.94 to 0.98. Straight bevel gear transmissions can deliver up to 370 kW and a peripheral speed of 5 m/s. The helical bevel gear transmission runs smoothly and the gear carrying capacity is high, but the manufacturing is difficult and the application is less. The curved bevel gear transmission runs smoothly, with a transmission power of up to 3,700 kW and a peripheral speed of over 40 m/s.
3. Hyperboloid gear transmission
Used to drive the drive between the axes. The single-stage transmission ratio can reach 10, the maximum to 100, the transmission power can reach 750 kW, the transmission efficiency is generally 0.9-0.98, and the peripheral speed can reach 30 m/s. The pinion cantilever mounting can be avoided due to the axial offset. Widely used in the transmission of cars and tractors.
4. Helical gear transmission
The gear transmission is used for inter-interlacing transmission, the transmission ratio can reach 5, the bearing capacity is low, the wear is severe, and the application is rare.
5. Worm drive
The main form of the staggered shaft drive, the axis stagger angle is generally 90 °. The worm drive can obtain a large transmission ratio, usually 8 to 80 for single stage, up to 1500 for transmission movement, 4500 kW for transmission power, 30,000 rpm for worm speed and 70 rpm for peripheral speed. m/s. The worm drive works smoothly, the transmission ratio is accurate, and it can be self-locking, but the transmission efficiency is less than 0.5 when self-locking. The worm gear has large sliding between the tooth surfaces, generates more heat, and has low transmission efficiency, usually 0.45 to 0.97.
6. Arc gear transmission
The gear transmission uses a convex and concave arc to make a gear transmission of the tooth profile. When the no-load is carried out, the two tooth profiles are point contacts. During the meshing process, the contact points move along the axis direction, and the longitudinal coincidence degree is greater than one to obtain a continuous transmission. It is characterized by high contact strength and load-bearing capacity, easy formation of oil film, no root cutting phenomenon, uniform tooth surface wear and good running performance; but sensitive to errors in center distance, cutting depth and helix angle, so Installation accuracy is high.
7. Cycloidal gear transmission
A gear train with a cycloid as a tooth profile. The contact between the tooth surfaces of the transmission is small, the wear resistance is good, and there is no root cutting phenomenon, but the manufacturing precision is high, and the center distance error is very sensitive. Used only in watches and meters.
8. Planetary gear transmission
Gear drive with moving axis. There are many types of planetary gears, and the performance of different types varies greatly. It is very important to choose the type according to the working conditions. Commonly used are ordinary planetary transmissions consisting of sun gears, planetary gears, internal gears and planet carriers, planetary gears with small tooth differences, cycloidal pin drives and harmonic drives. Planetary gears are generally assembled from parallel shaft gears. They are small in size and light in weight. The input shaft and output shaft can be on the same line. Its application is becoming more and more extensive.
Design criteria
Gear transmission For the five failure modes of the gear, the corresponding design criteria should be established separately. However, for the tooth surface wear, plastic deformation, etc., since the calculation methods and design data that are widely used in engineering and are effective have not been established, the current design of the gear transmission is usually only to ensure the tooth root bending fatigue strength and to ensure the tooth surface. The two criteria of contact fatigue strength are calculated. For high-speed and high-power gear transmission (such as aero-engine main drive, turbo generator set transmission, etc.), it is also calculated according to the criteria for ensuring the anti-adhesive ability of the tooth surface (refer to GB6413-1986). As for the ability to resist other failures, although the calculations are generally not performed, measures should be taken to enhance the ability of the teeth to resist these failures.
1. Closed gear transmission is known from practice. In closed gear transmission, the contact fatigue strength of the tooth surface is usually guaranteed. However, gears with high tooth surface hardness and low core strength (such as gears with 20 or 20Cr steel after carburizing and quenching) or brittle gears are usually used to ensure the root bending fatigue strength. If both gears are hard toothed and the tooth surface hardness is as high, it depends on the specific situation. Large-capacity transmissions, such as closed-gear transmissions with input power exceeding 75 kW, generate a large amount of heat, which is prone to poor lubrication and gear-to-gluing damage. In order to control the temperature rise, the heat dissipation capacity should also be calculated.
2. Open gear transmission open type (semi-open type) gear transmission should be calculated according to the two criteria of ensuring tooth surface anti-wear and root fracture resistance, but as mentioned above, the calculation method of tooth surface anti-wear ability So far, it is not perfect enough, so the split type (semi-open type) gear transmission is currently only designed to ensure the root bending fatigue strength. In order to extend the life of the open (semi-open) gear transmission, the modulus determined can be appropriately increased depending on the specific needs. As mentioned above, the dimensions of the rims, spokes, hubs, etc. of the gears are usually only for structural design, and no strength calculation is performed.
Noise Reduction Method Gear Transmission In order to prevent the reducer from passing the factory test, one of the reasons is that the reducer has intermittent high noise; it is tested with the ND6 precision sound level meter, and the low noise reducer is 72.3Db(A), which meets the factory requirements. The high noise reducer is 82.5dB (A), which does not meet the factory requirements. After repeated testing, analysis and improvement of the test, it is concluded that comprehensive management of all aspects of production must be carried out in order to effectively reduce the noise of the gear transmission.
1. Control gear precision: Basic requirements of gear precision: After practice, the gear precision must be controlled in GB10995-887~8, the line speed is higher than 20m/s gear, the pitch limit deviation, the ring gear radial runout tolerance, Tooth tolerance must be stable to 7 levels of accuracy. In the case of a 7-stage precision gear, the tooth should be reversed, and the root boss should be strictly guarded.
2, control the quality of raw materials: high-quality raw materials are the preconditions for the production of high-quality products, the company's largest amount of materials 40Cr and 45 steel to make gear. No matter the route, the raw materials must pass the strict chemical composition test, grain size measurement and purity evaluation after arriving at the factory. Its purpose is to adjust the heat treatment deformation in time to improve the quality of the tooth profile processing.
3. Prevent heat treatment deformation: After rough machining, the tooth blank becomes a precision forging, and it is normalized or quenched and tempered to achieve:
(1) softening steel parts for cutting processing;
(2) Eliminating residual stress;
(3) refining the grains and improving the structure to improve the mechanical properties of the steel;
(4) Prepare for organization in the end. It should be noted that in the normalizing or quenching and tempering treatment, it is necessary to keep the temperature of the furnace evenly, and to use the station tool to uniformly heat and cool the workpiece, and it is strictly prohibited to stack them together. For gears that need to be drilled to reduce weight, the drilling sequence should be arranged after heat treatment. The final heat treatment of the gear is made by high-frequency quenching of the tooth surface with less deformation of the part; the tooth surface obtained after the high-frequency quenching has high strength, hardness, wear resistance and fatigue limit, while the core still maintains sufficient plasticity and toughness. To reduce distortion. Tooth surface induction hardening should use a lower quenching temperature and shorter heating time, uniform heating, slow cooling.
4. Guarantee the accuracy of the tooth blank: The accuracy of the size of the gear hole is required to be distributed around the middle of the deviation value of the hole, and is set at ±0.003~±0.005mm. If it is out of tolerance and within the design requirements of the hole, it must be classified. , respectively, into the cutting process. The end face bounce and radial runout of the tooth blank are 6 levels, which are set in the range of 0.01~0.02mm.
5, cutting teeth processing measures: Outsourcing gear cutters must be tested, must meet the AA level requirements. After the gear cutter is sharpened, the radiality of the front edge of the tool, the adjacent circumferential pitch of the chip pocket, the maximum cumulative error of the chip pocket circumference, and the parallelism between the front of the cutter and the axis of the bore must be checked. Under the premise of not affecting the strength of the gear, increase the height coefficient of the crown, increase 0.05~0.1m, improve the tooth height coefficient of the cutter, and avoid the tooth root interference of the gear. The gear of M=1~2 adopts the tooth top rounding hob, and the rounding amount is R=0.1~0.15m. Eliminate the burr of the tooth tip and improve the tooth tip interference during gear transmission. The gear cutting equipment should be inspected once a year for accuracy. If it is not required, it must be repaired. The operator should also perform self-tests frequently, especially when the radial clearance of the machine tool spindle is controlled below 0.01 mm, the cutter shaft diameter is less than 0.005 mm, and the cutter shaft is moved below 0.008 mm. The installation accuracy of the tool: the tool radial runout is controlled below 0.003mm, and the end face is beaten below 0.004mm. The precision of the cutting tool, the gap between the outer diameter of the mandrel and the hole of the workpiece is guaranteed to be within 0.001~0.004mm. The thread on the mandrel must be ground by a threaded bed under the C-top positioning: verticality ≦0.003mm, diameter jump ≦0.005mm. The nut must ensure that the internal thread is clamped to the reference surface at one time. The parallelism of the washer is ≦0.003mm.
6, civilized production: Gear transmission noise more than 30% of the reasons are from burrs, bumps and injuries. Some factories remove burrs and bruises before the gearbox is assembled, which is a passive practice.
(1) Gear shaft parts, the hobbing rear tooth part is immediately put on a special plastic protective cover and then transferred to the next process, and the special plastic protective cover is put into the warehouse and shipped. (
(2) Carrying out the tooth decay process, reducing the tooth surface roughness, removing burrs, and preventing smashing, which can effectively reduce the gear transmission noise.
7. Take other materials and heat treatment and surface treatment methods:
(1) Powder metallurgy molding technology can be utilized to achieve high-frequency quenching of the teeth after gear shaping.
(2) The cast iron is used, and after the gear is cut, the soft nitriding treatment is performed.
(3) Using 40Cr material, after gear cutting work, it is treated by soft nitriding or tooth copper plating. In summary, to gear the gear transmission noise, the gear material and heat treatment are essential, the accuracy of the tooth blank is guaranteed, the gear precision is the key, and civilized production is the basis.
processing method
1. Grinding teeth: IT6~IT4→IT3, Ra: 0.8~0.2μm Principle: Forming method and forming method.
(1) Forming method grinding teeth IT6 to IT5, Ra: 0.8 to 0.4 μm, grinding with a forming grinding wheel, high productivity, low machining accuracy, and low application.
(2) Spreading method: Grinding teeth of the tapered surface: the tooth profile of the grinding wheel is the tooth shape of the imaginary rack, the workpiece is rolled to the right, and the right side of the first tooth groove is ground by the right side of the grinding wheel, from the root Grinding to the top; then the workpiece rolls to the left, grinding the left side of the lth groove on the left side of the grinding wheel, and grinding it from the root to the top. When both sides of the lth groove are completely ground, the grinding wheel automatically retreats. The workpiece, the workpiece is indexed and then rolled to the right to grind the 2nd tooth groove, so that the cycle is repeated until the full tooth is ground.
2, grinding teeth: IT7 ~ IT6, Ra: 1.6 ~ 0.2μm Equipment: grinding machine. Research tools: precision cast iron gears. Abrasive: Abrasive grain: 220#～240#, active lubricating oil Features: Same as dental caries, can only reduce surface roughness, can not improve tooth shape accuracy.
Parallel axis grinding method:
1. Process: The grinding wheel is parallel to the axis of the grinding gear. When grinding, the grinding wheel drives the grinding wheel to perform free meshing movement without backlash. The grinding gear is also axially reciprocated, and the grinding wheel is slightly braked. After a period of time, the grinding wheel and the wheel being rotated are rotated in opposite directions so that both sides of the tooth are uniformly ground.
2. Features: Since the sliding speed of the tooth surface is not uniform, the grinding amount is not uniform, and the sliding speed at the tooth top and the root portion is large, and the grinding amount is also large.
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