Function of a driveline

The basic function of a drive shaft is to transmit power from one point to another in a smooth and continuous action. In automobiles, trucks, and construction equipment, the drive shaft is designed to send torque through an angle from the transmission to the axle.

The drive shaft must operate through constantly changing relative angles between the transmission and the axle. It must also be capable of changing length while transmitting torque. The axle of a vehicle is not attached directly the frame, but rides suspended springs in an irregular, floating motion. This means the driveshaft must be able to expand, contract and change operating angles when going over bumps or depressions. This is accomplished through universal joints which permit the driveshaft operate at different angles, and slip joints, which permit contraction and expansion to take place.

This same concept holds true in other applications and in marine and industrial applications it has some added benefits. In most marine and industrial applications engines and gears are usually bolted down rigidly and coupled with a rigid shaft. This has been proven to cause vibrations and gear failure over time. The nature of a drive shaft is that it allows the engine and gear to move independent of each other, allowing for soft engine isolators and thus a reduction of vibration.

One thing that must be considered when using drivelines is that there are limits to the amount of angle that they will endure. Most universal joints will operate smoothly, and have an acceptable lifetime under 10 degrees. Over this angle and the problems of noise, vibration and shortened life can occur. The other limitation of a driveline is the fact that they will only operate through angles in one plane. A compound angle (or and angle in two planes) will cause a vibration, and lead to pre-mature failure and possible damage to other equipment. We have included a link to a torsional vibration analysis program that can help isolate and lessen the effects of a compound angle.

The double Cardan (aka constant velocity) universal joint will help in situations where there are excessively high, and in some cases compound angles. The Constant velocity type u-joint is a special design to accommodate necessary angles not compatible with single Cardan u-joints This type of joint will operate smoothly through angles up to 45 degrees in low speed applications. They are a problem solver, but are not with out problems themselves. They are expensive to buy and repair, and require extra maintenance and careful set up if they are to last.