ALT-2 What is the Constant Velocity Cv Joint
First, it was a universal joint. Next, a constant velocity universal joint, where two universal joints are coupled to make it function better was developed. Finally, a constant velocity (CV) joint came about perhaps to simplify or shorten the terminology but serves the same function as the constant velocity universal joint. The universal joint is used to couple a driving shaft to a driven shaft where the angularity of the line of drive is constantly changing. The driving shaft is turned by the engine through transmission gears and the universal joint transmits the power to a driven shaft at varying angles. The varying angles of the driven shaft is caused by the vehicle frame and wheels moving up and down due to road irregularities limited only by the vehicle suspension springs and linkages. Rear wheel drive vehicles use two or three universal joints in the drive line between the transmission gears and the differential gears that drive the rear wheels. In the case of a front wheel drive vehicle the use of a conventional universal joint is not possible because when operating at an angle with the yokes in the universal joint out-of-phase the velocity fluctuates in the drive shaft causing vibration. The problem is complicated by the fact that the joint must not only transfer driving power to the front wheels but also absorb the burden of steering on turns. To counter this problem, the constant velocity (CV) joint was developed. A constant velocity (CV) joint is packed with molybdenum disulfide grease for lubrication and dressed with a rubber boot for protection from dust, dirt, and moisture.
Essentially, a typical CV joint utilize rolling balls in grooves to obtain uniform motion. The rolling balls moves laterally as the joint rotates as it absorbs the force of rotating and turning the wheels during turns. The lateral move allows the point of contact between the two halves of the coupling to remain in the same plane which bisects the angle between the two shafts. That is how the velocity of the driven shaft is made constant.
The constant velocity (CV) joint is also used in four wheel drive vehicles. At least three of such joints are used in such vehicles. The engine transmission is coupled or geared to a transfer case to provide a power take-off to drive the shaft to the front wheels and the shaft to the rear wheels. It is important to note that the transfer case is provided with a shifting device so that the front drive can be disconnected when desired. Again, it must be emphasized that the constant velocity (CV) joint is to make better the function of driving a drive shaft at an angle without causing fluctuating velocity and vibration of the drive shaft. This is important not only in front wheel drive vehicles but also four wheel drive vehicles.
A true to life experience of mine regarding CV joints was the faster than normal deterioration of the CV joint when during one of my work employment years I was driving a front wheel drive and had to replace the CV joint once. At that point I realized that I have been driving to a parking garage everyday where the way to the upper floors is a spiral and turning is quite a torture for the CV joint. The bad CV joint manifested itself by a popping noise and shaking of my car whenever I make a turn. I found that the rubber boot had a tear and the grease dried. That was plain negligence and I learned a lesson. Check the rubber boot regularly.
