Gear reducers are generally used in low-speed, high-torque transmission equipment. They reduce the speed of electric motors, internal combustion engines, or other high-speed power sources by meshing a smaller gear on the input shaft with a larger gear on the output shaft. The ratio of the number of teeth on the smaller gear to the number of teeth on the larger gear is called the transmission ratio.
A speed reducer is a relatively precise piece of machinery used to reduce speed and increase torque. There are many types and models of speed reducers, each with different applications.
According to the transmission type, reducers can be divided into gear reducers, worm gear reducers, and planetary gear reducers; according to the number of transmission stages, they can be divided into single-stage and multi-stage reducers; according to the gear shape, they can be divided into cylindrical gear reducers, bevel gear reducers, and bevel-cylindrical gear reducers; according to the transmission arrangement, they can be divided into open type, split type, and coaxial type reducers.
To facilitate the selection of a speed reducer, the types, characteristics, and applications of several common speed reducers are listed for reference during the selection process.
1. Single-stage cylindrical gear reducer
Single-stage cylindrical gear reducers are suitable for reduction ratios of 3 to 5. The gear teeth can be spur, helical, or herringbone. The housing is typically made of cast iron, but can also be welded from steel plates. Rolling bearings are commonly used; sliding bearings are only used for heavy loads or ultra-high speeds.
2. Two-stage cylindrical gear reducer
Two-stage cylindrical gear reducers are available in three types: open type, split type, and coaxial type, with applicable reduction ratios of 8 to 40.
Expanded type: High-speed stage with long-tailed helical gears, low-speed stage can be spur or helical gears. Due to the asymmetrical arrangement of gears relative to bearings, the shaft rigidity is required, and the torque input and output ends should be far away from the gears to reduce uneven load distribution along the tooth width caused by shaft bending deformation. It has a simple structure and is the most widely used.
Split-flow type: Generally uses a high-speed stage for split-flow. Because the gears are symmetrically arranged relative to the bearings, the forces on the gears and bearings are more evenly distributed. To minimize the total axial force on the shaft, the helical directions of the two pairs of gears should be opposite. The structure is more complex and is often used in high-power, variable-load applications.
Coaxial type: The axial dimension of the reducer is relatively large, the intermediate shaft is relatively long, and the rigidity is relatively poor. When the two large gears are immersed in oil to similar depths, the load-bearing capacity of the high-speed stage gear cannot be fully utilized. It is often used in applications where the input and output shafts are coaxial.
3. Single-stage bevel gear reducer
Single-stage bevel gear reducers are suitable for reduction ratios of 2 to 4. The transmission ratio should not be too large to reduce the size of the bevel gears and facilitate machining. They are only used in transmissions where two axes intersect perpendicularly.
4. Bevel and cylindrical gear reducers
Bevel and cylindrical gear reducers are suitable for reduction ratios of 8 to 15. Bevel gears should be placed in the high-speed stage to reduce their size. Bevel gears can be spur or helical. Cylindrical gears are mostly helical to partially counteract the axial force of the bevel gears.
5. Worm gear reducer
The main types include cylindrical worm gear reducers, circular arc toroidal worm gear reducers, conical worm gear reducers, and worm-gear reducers, with cylindrical worm gear reducers being the most commonly used.
Worm gear reducers are suitable for reduction ratios of 10 to 80. They have a compact structure and a large transmission ratio, but low transmission efficiency, making them suitable for low-power, intermittent operation applications. When the worm's circumferential speed V ≤ 4~5 m/s, the worm is positioned below, resulting in better lubrication and cooling conditions; when V ≥ 4~5 m/s, oil churning losses are greater, and the worm is generally positioned above.
6. Planetary gear reducer
Due to their structure, planetary gear reducers have a minimum single-stage reduction of 3 and a maximum of generally no more than 10. Common reduction ratios are 3/4/5/6/8/10. The number of gear reducer stages generally does not exceed 3, but some custom-made gear reducers with large reduction ratios have 4 stages.
Compared to other speed reducers, planetary speed reducers feature high rigidity, high precision (within 1 minute for a single stage), high transmission efficiency (97%-98% for a single stage), high torque, low volume ratio, and lifetime maintenance-free operation. Because of these characteristics, planetary speed reducers are mostly installed on stepper motors and servo motors to reduce speed, increase torque, and match inertia.
