Force Plus Force: A Comprehensive Collection of Knowledge on Gear Reducer Reduction Ratios

    I. Main Overview

The reduction ratio, which is the transmission ratio of a speed-reducing device, is a type of transmission ratio. Gear reducer Among these, the reduction ratio is a very important parameter. It refers to the ratio of the instantaneous input speed to the output speed in the reduction mechanism and is denoted by the symbol “i.”

The general method for expressing a reduction ratio is to use the input speed and output speed, with 1 as the denominator, connected by a colon (:). For example, if the input speed is 1500 r/min and the output speed is 25 r/min, the reduction ratio would be: i = 60:1. Typically, the reduction ratios marked on conventional减速 mechanisms reflect the actual reduction ratio; however, some special cases... Gear reducer such as harmonic reducers or wave generators Gear reducer Sometimes, rounding is used for integer approximation, and the denominator is omitted—for example, the actual reduction ratio might be 28.13, but it’s typically labeled as 28.

        II. Calculation Method

1. Define the calculation method: Gear ratio = Input speed ÷ Output speed ，， The ratio of the input speed to the output speed of a gearbox is as follows: If the input speed is 1500 r/min and the output speed is 25 r/min, then the reduction ratio is: i = 60:1.

2. Gear System Calculation Method: Gear reduction ratio = Number of teeth on the driven gear ÷ Number of teeth on the driving gear (If it’s a multi-stage gear reduction, simply divide the number of teeth on the driven gear by the number of teeth on the driving gear for each meshing pair of gears, and then multiply the results obtained.)

3. Calculation method for belt, chain, and friction wheel reduction ratios: Reduction ratio = Diameter of driven pulley ÷ Diameter of driving pulley.

        3. Principles for Allocating the Reduction Ratio

The basic principle for allocating transmission ratios is: ：

1. Ensure that the load-carrying capacities of transmission stages at all levels are approximately equal (generally referring to tooth surface contact strength).

2. Ensure that the large gears in transmission systems at all levels are immersed in oil to roughly the same depth, thereby simplifying lubrication.

3. Ensure the reducer has the smallest possible overall dimensions and weight.  

    IV. Essential Common Sense About Gear Ratios

First, determine the type of gearbox you need. Then, specify the input power and the required output torque. Next, based on the input shaft speed and the desired output shaft speed, calculate the gearbox’s reduction ratio. Finally, determine the service factor according to actual operating conditions, such as daily working hours, impact loads, switching frequency, and so forth.

        Try to select a reduction ratio that is as close as possible to the ideal value: Reduction ratio = Servo motor speed / Output shaft speed of the reducer. 。

Torque Calculation: For the lifespan of a gearbox, torque calculation is crucial. It’s important to ensure that the maximum torque value under acceleration (TP) does not exceed the gearbox’s maximum allowable load torque.

Gearbox Model Selection and Precautions: The applicable power typically corresponds to the rated power of commonly available servo motor models. The gearbox boasts high versatility, with service factors consistently remaining above 1.2. However, you can also make your selection based on your specific requirements. When choosing a servo motor, the diameter of its output shaft must not exceed the maximum shaft diameter specified in the table.

If, after torque calculations, the rotational speed can meet normal operating requirements but still falls short when the servo is running at full output, it is essential to implement current-limiting control on the driver side of the motor or to install torque protection on the mechanical shaft.

Determine the required motor specifications based on the selected machine model, load torque, transmission ratio, and output speed.

1. Identify the equipment in which the gearbox will be used, so as to determine the safety factor SF (SF = Rated power of the gearbox divided by the motor power), as well as the installation configuration (e.g., right-angle shaft, parallel shaft, hollow-shaft keyway output, hollow-shaft locking disc output, etc.).

2. Provide the motor power and the number of poles (whether it’s a 4P, 6P, or 8P motor).

3. Ambient temperature around the gearbox (determines the verification of the gearbox’s thermal power rating)

4. Verification of the radial and axial forces acting on the output shaft of the gearbox. Both the axial force and the radial force must be provided.  

        V. Relevant institutions for the reduction ratio

      1. Speed-reducing transmission device

Main components include: input gear shaft, bearings, large gear, key, output shaft, and others.

Note: The deceleration and transmission functions are accomplished by the input gear shaft, large gear, key, and output shaft.

        2. Positioning and connecting device

Main components: bolt fasteners, washers, nuts, and pins.

Note: To enable repeated disassembly and reassembly of the reducer’s housing and cover while ensuring installation accuracy, this reducer employs a combination of tapered pins for positioning and bolted connections between the housing and the cover.

    3. Lubrication device

Main components: housing, lid, gears, bearings.

Note: The lubrication points of the reducer include the gear teeth and the bearings. The gear teeth are lubricated by the large gear itself, which carries lubricant for self-lubrication. As for the bearings, the oil flung off by the large gear flows along the inner wall of the housing cover into an oil groove located at the top of the housing, and then flows from the oil groove into the bearings to provide lubrication.

       4 Sealing device

Main components: transparent cover, sealed cover.

Note: To prevent lubricant leakage, gear reducers generally do not feature sealing devices. The gear reducer described here employs an embedded sealing system, which consists of two open covers and two closed covers to ensure effective sealing.

    5. Axial positioning device

Main components: transparent cover, sealed cover, output shaft, input shaft, adjusting washer, and locating sleeve.

Note: The axial positioning of the input gear shaft is achieved by means of sealed end caps and through-type end caps, with the clearance adjusted using shims. The axial positioning of the output shaft is accomplished by sealed end caps, through-type end caps, and a locating sleeve at both ends; clearance adjustment is performed using adjustable washers.  

        6. Observation device

Main component parts: observation port cover, oil level indicator assembly.

Note: The observation device consists of an observation port located above the box lid and an oil-level indicator assembly situated in the lower-left part of the box body. The observation port is primarily used to monitor the operation and lubrication condition of the gears. The oil-level indicator serves to ensure that the lubricant level inside the box remains at an appropriate height. If the oil level is too high, it will increase the resistance to the rotation of the large gear, resulting in excessive loss of transmission power. Conversely, if the oil level is too low, the gears and bearings will be inadequately lubricated—or even completely unlubricated—leading to rapid wear and damage of the reducer.

      7. Ventilation balance device

Main component: Ventilation screw.

Note: The vent screw located on the top of the box cover is used to equalize the air pressure inside and outside the box, keeping them roughly the same. Otherwise, excessive internal pressure would increase the resistance to movement and also lead to increased leakage of lubricating oil.

        VI. Main Functions

1. While reducing the speed, increase the output torque accordingly. The torque output ratio is calculated by multiplying the motor’s output torque by the reduction ratio; however, be sure not to exceed the reducer’s rated torque.

2. Reducing the speed also reduces the load’s inertia; the reduction in inertia is proportional to the square of the transmission ratio. You can take a look—most motors come with a specified inertia value.