Constant-velocity joint : Specific classification and principle

1. The principle, types and usage scenarios of universal joints

The so-called universal joint, also known as a Constant-velocity  joint, is a mechanism that realizes variable-angle power transmission and is used for positions where the direction of the transmission axis needs to be changed. And the installation positions of different driving wheels are different. For example, on a vehicle with front-engine rear-wheel drive, the universal joint transmission is installed between the transmission output shaft and the input shaft of the drive axle final reducer; while the vehicle with front-engine front-wheel drive omits the drive shaft, and the universal joint It is installed between the front axle half shaft and the wheel, which is responsible for both driving and steering.

Obviously, universal joints are also divided into very many types, there are three-pin shaft, cross shaft, ball fork, as well as our ball cage and so on. At the same time, universal joints are divided into two types: ordinary universal joints and constant velocity joints, and the ball cage type is the commonly used constant velocity joint.

When the deflection angle of the car is very large, reaching more than 40°, the traditional ordinary universal joint with a small deflection angle cannot be used. When the deflection angle of ordinary universal joints is large, the speed and torque will fluctuate greatly. It is difficult to transmit the power of the car engine to the wheels smoothly and reliably, and it will also cause vibration, shock and noise (NVH) of the car. It is time to use a constant velocity joint with a large deflection angle, smooth power transmission, and uniform angular velocity.

2. the specific structure of the ball cage type constant velocity joint

The ball cage (cv joint), the full name of the ball cage type constant velocity joint, is generally divided into two pairs (inner and outer), with a ball cage dust cover (cv boot). It is mainly composed of sliding sleeve, three-way shaft, transmission shaft, star-shaped sleeve, cage, and bell-shaped shell. Because the constant velocity universal joint transmits heavy driving torque, bears heavy load, high transmission precision, large demand, and is a safety part, its main parts are all made of precision forgings. Compared with other constant velocity joints, it has the advantages of strong bearing capacity, compact structure, and convenient disassembly and assembly, so the ball cage has gradually become the most widely used constant velocity joint.

• The composition of the outer ball cage: 1. Bell shell; 2. Inner star wheel; 3. Cage; 4. Steel ball; 5. Dust cover; 6. Beam ring; The ingredient is molybdenum disulfide).

• Composition of inner ball cage: 1. Bell shell; 2. Trident bearing or steel ball. (There are two differences here); 3. Dust cover; 4. Beam ring; 5. Grease (different from general butter, the main component is molybdenum disulfide).

The dust cover is also a key component in the ball cage product, its main function is to prevent dust from entering the ball cage and block the outflow of butter in the ball cage. Special high temperature grease must be used in the ball cage and cannot be replaced by other greases.