What is a UNIVERSAL JOINT - Cardan or Constant-velocity Joint?

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The Universal joint is a mechanical device that allows one or more rotating shafts, whose axes are inclined to each other, to be linked together, allowing the transmission of torque and rotary motion. For this reason, universal joints are classified as torque transmission devices.
The invention of this type of joint dates back to the 3rd century BC, thanks to some Greek scientists such as Philo of Byzantium, who mentioned this type of joint in his work “Belopoeica”.
But it is only in 1545 that the famous Italian mathematician and physicist Gerolamo Cardano rediscovered this important device, which is also called Cardan joint.
The Universal Joint consists of an intermediate cross-pin member, simply known as the Cross. The size of the Cross is determined in order to obtain the best compromise between the dynamic features of the rotating elements of the joint, and the flexural properties of its pins.
The cross links two yoke shafts together. Each pair of yoke is positioned at right angles to the other. The cross allows each Yoke to rotate around the Y and Z axes. The yoke shaft connected to the engine is called Input Shaft, while the other one is called Output Shaft. The input shaft transmits it rotational movement to the output shaft.
The Yokes are designed to overcome any elastic deformations, and they also keep aligned the bearing seats of the Cross. These yokes are usually made of steel and they are manufactured to stringent quality and safety standards. The angle between the two shafts is called “operating angle”. With standard yokes which rotate for short periods of time, it is possible to reach an operating angle of 45 degrees. While for continuous use, an operating angle of 35 degrees shall not be exceeded.
The transmission ratio of the yokes does not remain constant over time, but it has a smooth periodic oscillation with a sine-wave pattern. This means that the speed of the input shaft will never be equal to the speed of the output shaft; the consequence of this phase shifting causes vibrations. The greater the operating angle, the greater the vibration willl be.
To overcome these issuses, the Double universal joint can be used to accommodate the misalignment between two parallel shafts.
The Telescopic Universal Joint is however used in the agricultural sector, especially on vehicles such as tractors. This consists of two simple joints connected by a telescopic shaft, which is able to acomodate variations in lenght between the tractor and its attachment. This variations can occur during the tractor maneuvers, due to the roughness of natural terrain.
In the industrial sector, the universal Joint is used to transmit rotary motion to many devices, such as: conveyor belts. It can also be used to operate the different cutters of a moulder machine.
The Constant-velocity joint on the other hand, has a slightly different working principle; it always links an input and an output shaft together, but unlike the Universal Joint, this one has the ability to keep the Transmission ratio constant over time, regardless of the rotation angle of the shaft.
Usually a Constant-velocity joint has an external protection. Its heart is represented by the inner core, through which the torque and the rotary motion are transmitted. The connection between the two shafts takes place thanks to a series of steel balls placed one by one inside a cage. Thanks to this cage the balls are free to rotate indipendently inside its grooves, allowing the articulation of the shafts as well as the transmission of motion. This type of joint is protected by a rubber boot, a "CV gaiter", usually filled with molybdenum disulfide grease. The rubber boot infact protects the joint from water and dust damages over time.
Many people may not know what a Constant-velocity joint is or what it is used for, even though it is a very important devide for every vehicle.
Constant velocity joints in fact are mainly used in vehicles with front wheel drive, but also in several modern rear wheel drive cars with independent rear suspension.
In this last case, these joints are used at the ends of the rear axle halfshafts or on the drive shafts.
10 years in the industrial supplies sector, have led JAES to become a qualify partner for some of the most important mechanical joint manufacturers, offering a wide range of different joint types, such as...
We can conclude by saying that in the vast industrial sector, from energy, to food, from agriculture to woodworking, the universal Joint is a very important device, which plays a leading role in the modern industries all over the world.