Universal Joints

Universal joint is a mechanical device that can achieve power transmission between two non coaxial shafts. Its core function is to allow the two connected axes to deflect relative to each other within a certain angle range, while maintaining effective torque transmission.

Typical structural composition:

• Cross axis: a core component with four shaft necks distributed in a cross shape
  

• Fork head components: usually have two, connecting the input shaft and output shaft respectively
  

• Bearing component: supports cross axis rotation, reduces friction
  

• Lubrication system: ensuring long-term reliability of operation

Compared with traditional rigid couplings, the prominent feature of universal joints is their ability to compensate for large shaft to shaft angular deviations (usually up to 15 ° -45 °), while allowing for a certain degree of axial and radial displacement, making them an ideal choice in complex transmission systems.

The working principle of universal joint is based on spatial geometric kinematics. When there is an angle between the input shaft and the output shaft, the rotation of the cross axis converts the uniform rotation of the input shaft into non-uniform rotation of the output shaft, and this speed fluctuation intensifies with the increase of the angle between the two axes.

Key mechanical properties:

• Speed fluctuation: The output shaft speed varies periodically, and the fluctuation amplitude is proportional to the sine square of the deflection angle
  

• Dual compensation: using two universal joints arranged in a specific way to eliminate speed fluctuations (such as a "Z" - shaped arrangement)
  

• Load bearing capacity: The strength of the cross shaft and bearings determines the maximum transmitted torque
  

• Efficiency loss: Typically, the transmission efficiency can reach 98% -99.5%, with lower efficiency as the angle increases

Modern universal joints have significantly improved the limitations of traditional structures through optimized design, such as using involute splines, special bearings, etc., resulting in a significant increase in maximum working angle and transmission efficiency.

With the development of industrial demand, universal joints have evolved into various structural forms, each with its own applicable scenarios and technical characteristics.

• Cross axis universal joint
  Basic type: Standard cross axis structure, low cost, most widely used
  Heavy duty: reinforced design, used for heavy-duty applications such as metallurgy and mining
  Miniature: Small scale design for precision instruments, such as camera gimbals

• Ball cage constant velocity universal joint
  Adopting a spherical cage and multiple steel ball structures
  Realize true constant speed transmission without speed fluctuations
  Widely used in front wheel drive systems for automobiles

• Double universal joint
  Two cross axis universal joints are connected through a spline shaft in the middle
  Can compensate for larger offset and eliminate speed fluctuations
  Used for long-distance transmission or situations requiring large deflection

• Flexible universal joint
  Replacing some metal components with elastic elements
  Has vibration and noise reduction characteristics
  Suitable for precision transmission and occasions that require vibration absorption

Universal joints, due to their excellent performance, have almost penetrated into all fields of mechanical transmission:

• Automotive industry: transmission shaft, steering system, four-wheel drive system
  

• Construction machinery: Transmission systems for excavators, loaders, cranes, and other equipment
  

• Steel metallurgy: heavy equipment such as rolling mills and continuous casting machines
  

• Shipbuilding industry: propulsion shaft system, servo system
  

• Aerospace: Helicopter transmission system, aircraft control surface actuators
  

• Energy equipment: wind turbine yaw system, oil drilling rig
  

• Industrial robots: Joint transmission, precision positioning system

In the field of new energy, especially in wind turbines, universal joints play a key role in pitch and yaw systems, and their reliability and durability directly affect the overall performance of the machine.

Selection considerations:

• Torque demand: Calculate maximum working torque and peak torque
  

• Speed range: Consider the critical speed limit
  

• Deviation angle: angle requirements under static and dynamic conditions
  

• Environmental conditions: temperature, humidity, corrosiveness, etc
  

• Space limitations: Installation size and weight constraints

Installation and maintenance suggestions:

• Ensure that the alignment error of the two end axes is within the allowable range
  

• Regularly check the lubrication condition and replenish or replace lubricating grease according to specifications
  

• Monitor abnormal vibrations and noise to promptly detect bearing wear
  

• Avoid overloading and impact loads to prevent cross axis fracture
  

• Regularly check the wear of the spline fitting parts

Modern intelligent maintenance technology has begun to be applied to high-end universal joints, achieving predictive maintenance through vibration analysis, temperature monitoring, and other means, greatly improving equipment reliability and service life.

As a key component of mechanical transmission systems, the technological progress of universal joints directly affects the development level of the entire equipment manufacturing industry. In the future, with the continuous emergence of new materials and processes, universal joints will continue to demonstrate their unique value as "universal joints" in a wider range of fields.