Constant Velocity Joint

A Constant Velocity Joint (CV Joint) is a vital component in an automotive drivetrain system. Its primary role is to connect two intersecting shafts and ensure smooth power delivery at the same instantaneous angular velocity.

Think of it as the drivetrain’s articulated joint. In a conventional cross-type universal joint (Cardan joint), operating at an angle causes the driven shaft's rotational speed to fluctuate, generating vibration and noise. A CV joint overcomes this drawback through a clever geometric design, making it particularly well-suited for driven wheels that require large steering angles.

Working Principle: Clever Geometric Engineering

The constant velocity characteristic of a CV joint stems from a unique geometric principle: all drive contact points (such as steel balls) always lie precisely on the bisecting plane of the angle formed between the two shafts. This keeps the angular velocity of the drive points permanently synchronised, resulting in smooth, pulsation-free power delivery.

Main Types and Construction

Currently, the most common CV joints are broadly categorised into ball-and-fork and ball-cage types, with the ball-cage design being the most widely adopted.

1. Ball-Cage CV Joint
This is the current industry mainstream, named after the internal "cage" that houses the steel balls. It boasts a high load-bearing capacity and a compact design. Based on whether it allows axial movement, it is further divided into two configurations:

• Fixed Type (RF Joint): Fitted primarily at the wheel hub (outboard end), it accommodates a generous articulation angle during steering of up to 47°, though it does not allow for axial plunge.

• Plunging Type (VL Joint): Positioned predominantly at the differential (inboard end). In addition to delivering power, it slides axially to compensate for changes in driveshaft length as the suspension travels over bumps.

2. Ball-and-Fork CV Joint
Featuring a relatively simple construction, it typically accommodates a maximum operating angle of around 32° to 33°. However, because only a portion of the steel balls bear the load during operation, it experiences faster wear and is far less common than the ball-cage design.

Additional Note: Beyond these mainstream designs, newer configurations with superior performance are also available, such as the Tripod Joint. Utilising precision rollers and needle bearings, it excels at minimising sliding resistance and reducing contact stress.