CONSTANT VELOCITY JOINT

A constant velocity joint or CV joint is a mechanical coupling that transmits rotational power from a drivetrain to the wheels at constant angular velocity regardless of the operating angle between the input and output shafts.

The constant velocity joint consists of an inner race, outer race (housing), ball bearings or rollers and a cage that keeps the balls in precise positions. The geometry of the joint is designed so that the contact points always lie on the bisecting plane between the two shafts. This bisecting plane properly ensures that any angular difference between input and output is equally divided, canceling out the velocity fluctuations that plague simpler joints. Thus by this means a constant velocity (CV) joint transmits power smoothly at varying angles to front wheel drive vehicles.

The advantages of constant velocity joints are; they allow for smooth power delivery as it eliminates the speed fluctuations inherent in simple Universal joints, thereby reducing to the barest minimum dangerous resonant vibrations and drive train pulsing. They have high angular capability especially as shown by Rzeppa joints another variant of constant velocity joint, which can operate at up to 30 degrees, enabling tight steering turns while maintain drive. They are compact, lightweight and enable front wheel drive. They are quiet in operation, durable and compatible with the suspension travel without binding.

The disadvantages of constant velocity joints are; the rubber constant velocity booth tears easily from road debris, age or improper handling causing dirt to enter the joint, ultimately rapid deterioration and damage to the joint. They have limited torque capacity, angle limitation, heat sensitivity, replacement complexity and above all are expensive to manufacture, operate and maintain.

Constant velocity joints find applications in the following: Front wheel drive (FWD) vehicles , where they are used for both inner and outer ends of front drive axles; all-wheel drive (AWD) , where they are used for all four axle shafts and sometimes for the front/rear propeller shafts; four wheel drive (4WD), where they are used for the front axle half-shafts, enabling steering plus power; rear wheel drive (RWD), where they are used for the independent rear suspension half-shafts; electric vehicles (EV) where they are used as the motor to wheel half shafts (high torque demand); heavy trucks/SUVs where they are used for the front live axles in solid axle 4WD configurations; racing cars where they are used to provide high angularity, high RPM constant velocity joints on all corners.

The future of constant velocity joints is based on the advances and development of the following technologies; reinforced ball bearing, new steel alloys and optimized case geometries; grease free and reduced lube designs; integrated motor constant velocity shaft system for electric vehicles and advanced boot materials; the next generation constant velocity joint may incorporate embedded torque, speed and wear sensors, feeding real time data to the vehicle management system thereby enabling predictive maintenance alerts before failure occurs; advances in geometry and materials will push the maximum operating angles beyond 50 degrees, thereby supporting new vehicle architectures such as steer by wire systems with extreme wheel articulation angles; the use of titanium alloys, carbon fiber-reinforced housing and ceramic ball bearings in performance and motorsport applications, hence reducing unsprung mass in vehicles.

 

SOURCES:

• Universal joints and drive shafts: Analysis, design, applications by Hans Christoph, Seherr-ThoB, Friedrich Schmelz and Erich Aucker.
• Automotive drivetrain and manual transmission by Keith Santini.
• Automotive technology: A systems approach by Jack Erjavec and Bob Thompson.
• Kinematic and dynamics of machinery by Charles E. Wilson and J. Peter Sadler.
• Fundamentals of vehicle dynamics by Thomas D. Gillespie.