Gear transmission system is widely used in industry, transportation and energy fields, and its efficiency directly affects the energy consumption and operation cost of equipment. In practice, gear transmission efficiency is affected by many factors, such as rolling friction, oil film shear loss, tooth surface lubrication state. This paper will analyze the main sources of gear transmission loss and explore how to improve gear transmission efficiency by optimizing tooth shape and lubrication technology.

1. Definition of gear transmission efficiency

Gear transmission efficiency refers to the ratio of input power to output power, expressed by the formula:

among:

η：Gear transmission efficiency is (%)

Pout：output power (W)

Pin：interiorinput power (W)

Ideally, the gear transmission should be loss-free, but in the actual operation, the transmission process will be affected by friction, lubricating oil shear and other factors, resulting in energy loss.

• The main source of gear transmission loss

Gear transmission loss mainly comes from the following aspects:2.1 friction loss of rolling and sliding

During gear engagement, there is rolling and relative sliding between the tooth surface, which will cause friction loss. The size of the friction loss depends on:

Gear material (surface hardness, lubrication adaptability)

Roughness (smoother, less friction loss)

Enging mode (inclined gear has less sliding friction than straight gear)

2.2 shear loss of oil film

Lube oil plays friction and cooling effect in gear transmission, but also brings viscosity shear loss. When the gear operates at a high speed, the oil film between the tooth surface needs to overcome the internal shear stress, resulting in energy loss. Affected factors include:

Lubricant viscosity (high viscosity oil loss, low viscosity oil loss is small but may lead to boundary lubrication)

Oil film thickness (appropriate thickness reduces direct contact friction)

Gear surface speed (higher the speed, more the shear loss)

2.3 Bearing friction loss

In the process of gear transmission, the bearing assumes the role of rotating support, and the friction between the internal rolling body and the grease will produce a certain energy loss. Bearing friction can be reduced by:

Low-friction bearings (such as ceramic bearings, precision ball bearings)

Use a low-viscosity lubricating grease to reduce the rolling friction

2.4 Mixing loss of gas and oil inside the gear

High-speed rotating gears stir the lubricating oil and air to form an oil mist or bubbles, factors that cause additional fluid dynamic loss. The following measures may be taken to reduce the agitation loss:

Optimize the gearbox oil level to avoid excessive oil hindering the gear movement

Use oil mist lubrication to reduce the volume of lubricating oil directly contacting the gear.

3. Methods to improve gear transmission efficiency

3.1 Optimize the tooth shape to reduce the friction loss

Gear tooth shape design has a great influence on the transmission efficiency. Optimizing the tooth shape can reduce the friction loss and improve the engagement stability. Common optimization methods include:

�� Increase the pressure Angle (such as 25 instead of 20): can reduce the sliding friction, improve the bearing capacity �� use the ute shape (Profile Modification): reduce the top interference, improve the engagement efficiency �� use high precision tooth grinding process: reduce the surface roughness, reduce friction

3.2 Select the appropriate lubrication method

Lubrication has a significant influence on gear transmission efficiency, and appropriate lubrication methods should be selected in different application scenarios:

✅ High speed gear transmission (such as rail transit gear box): it is recommended to use synthetic oil (PAO or ester base oil), low viscosity, low shear loss

✅ overloaded low speed gear (such as wind power gear box): it is recommended to use high extreme voltage additive lubricating oil, reduce tooth surface wear

✅ high temperature gear: it is recommended to use solid lubrication coating (such as MoS ₂), improve wear resistance

3.3 Use the highly efficient bearing to reduce the bearing loss

✅ Using ceramic mixed bearings (Hybrid Ceramic Bearings), reduce rolling friction

✅ optimize pretension force, reduce additional friction loss

✅ use fluid dynamic pressure bearings, suitable for high-speed gear system

3.4 Design the gearbox structure with low mixing loss

✅ Adopt oil fog lubrication system to reduce oil resistance

✅ Design the internal structure of streamlined gearbox, reduce wind resistance and oil disturbance

✅ Optimize the design of gearbox vent hole to reduce internal airflow loss

4. Efficient design practice of rail transit gear box

In the field of rail transit, the efficient design of the gearbox can effectively reduce the train energy consumption and improve the operation economy. Here are some of the optimization cases:

�� High-speed EMU gear box

Low-friction coated gear is applied to reduce sliding loss

Use the high-precision grinding gear to reduce the friction coefficient of the tooth surface

A spray lubrication system was used to optimize the oil spray film thickness

�� City subway gear box

Low-shear loss lubricant is selected to reduce power loss

• Adopt the root trimming optimization to improve the engagement efficiency

�� Gear transmission efficiency is affected by many factors, and the main loss sources include tooth surface friction, lubricating oil shear, bearing friction, and gear mixing loss.

�� Optimizing the tooth shape, choosing the appropriate lubrication mode, reducing the bearing friction and optimizing the gearbox structure are the key measures to improve the transmission efficiency.

�� Rail transit gear boxes shall be designed with efficient lubrication, precision manufacturing and optimized structural design to reduce energy loss and improve the overall system efficiency.