Cardyfren, Cardan Transmissions

The following is intended, in particular, to help the design and project engineer develop optimum in-service conditions for any intended use of propeller shafts and thereby obtain perfect functional reliability and a prolonged service life of the drive arrangement. It is often possible at the design stage to facilitate the incorporation of a universal drive, most desirably for efficiency reasons, as a standard type. We should be very pleased to counsel you on all your drive problems.

Inflection angle and service life

The distinguishing feature of a universal joint is its ability to transmit rotary motion through a constant or varying angle ß. The inflection angles shown on the dimensional sheet can safely be obtained where special circumstances necessitate their use. Generally, it should be the aim to keep the operating inflection angle as small as possible, considering that the useful life of antifriction bearing joints is roughly reduced by half with every five degree increase of the inflection angle.

Where a universal joint has angles in the horizontal and vertical planes at the same time, the resulting angle can be calculated from the components ßh and ßv, or it can be gathered from the diagram , which gives sufficient accuracy in most cases.

Example: ßv = 25°, ßh = 15°, ß = 28.3°

Kinematics

The universal joint works in accordance with a certain kinematic law: With the driving shaft at a constant angular velocity w1 the angle at the joint results in periodic variations in w2. This angular velocity on the driven side passes through peaks and valleys twice per revolution, their absolute amounts progressively increasing with the inflection angle. With constant output, the torques are inversely proportional to the angular velocities, so that the resulting extremes for the driven shaft are as follows:

Turning Angle	0 and 180	20 and 270

This kinematic unevenness is critical if two shafts positioned at an angle of inflection are linked by a single joint. The mid-section of a propeller shaft located between two joints can also induce vibration in the power train due to acceleration and deceleration. Small angles of inflection are therefore important also to this shaft configuration, especially in the high-speed range. Therefore, to ensure that propeller shafts run smoothly and with little vibration, the product of n·ß (speed x angle of inflection) should remain within empirical limits.

where m [kg] is the mass of the propeller shaft. Where a single joint is used, it is all-important to check that the differential angle of the dissimilar rotation and the resulting mass forces are within permissible limits for the given application.

Arrangement of propeller shafts

Two joints allow to compensate the periodic fluctuations of the angular velocity of a single joint. With reference to the following figure, this is achieved by locating the inner pin axes, shafts 1, 2 and 3 in a single plane which makes identical inflection angles of both joints. Z and M arrangements have the same kinematic value.

On the other hand, homokinetic transmission of the rotary motion is also possible when shafts 1, 2 or 3 are not in one plane. However, identical spatial inflection angles will be needed in this situation. This is the case, if one view shows the M shape whereas the other is of Z shape. In this situation, the joints must be rotated relative to each other until the inner joint axes are located in their respective inflection planes. This configuration can only be used for propeller shaft drives consisting of single joints. Standard universal joints are not suited in this case. Basically, all inflection angles in a propeller shaft should be the same. This may not be possible in some cases. Then it should be decided if the remaining degree of angular irregularity can be tolerated. Exact figures for the permitted difference between the inflection angles on the input (driving) side and the output (driven) side cannot be specified because the degree of angular irregularity strongly depends on the absolute magnitude of the angle. Other factors that need to be considered are speed and stiffness, i. e., the drive system's torsion spring coefficient. Where the propeller shafts are arranged one after the other in a line, the following combinations are recommended:

Propeller shaft and intermediate shaft with elastic bearing

Propeller shafts with double support bearing

To avoid dissimilarities and vibrations connected with them, it is advisable, in the appropriate circumstances, to install the individual propeller shafts offset to one another (90°).

Arrangement of double jointed propeller shafts

Used especially for pivoted rigid axles, the uncentred-joint version requires, in radial direction, a statically determined support of the two connected shafts. One of them has to be fixed axially, while it must be ensured, that the other shaftcan move by the amount lv. The pivot point S should coincide with the centre of the joint or be shifted towards the side of the axially movable shaft.

In centred-joint double-jointed propeller shafts, the centring acts as an inner support of the constant velocity joint. Unlike the uncentred arrangement, this one eliminates the need for the bearing on the joint end of the one shaft, but necessitates the arrangement of another joint on the other end. The design should allow axial displacement for one of the two connecting drive forks.

Transverse whirling speed

Every propeller shaft has a transverse whirling speed which must never be reached during operation. This depends mainly on the distance between the two joints and on the flexural strength of the tube used. Also, it is influenced by the wear and tear of the shaft, especially of the splined connection of the telescopic section. Excessive speed causes vibration and premature failure of the propeller shaft and the connected parts of equipment. The transverse whirling speed for propeller shafts can be calculated as follows:

D = tube outer diameter, cm
d = tube inner diameter, cm
l = distance between joints, or distance between joint and intermediate bearing, cm

The operating speed should not exceed 80% of the critical speed calculated, otherwise the application would require, instead of one propeller shaft, the arrangement of two propeller shafts with an intermediate bearing, a so-called train of propeller shafts. This involves certain requirements with respect to the inflection angle. For advice contact our applications engineers.

Limitations in terms of length and speed

The length of tubular propeller shafts is limited by the speed beyond which inflection is likely, or simply by the limits set in production. The largest length available is L = 6000 mm, for shafts that need balancing it is L = 4500 mm. Larger length options on request.

Balancing of propeller shafts

Unless some low speed is required, as a rule, propeller shafts are balanced dynamically. Dynamic balancing guarantees smooth running of the propeller shaft, minimizing the load on the bearings caused by centrifugal forces. Depending on the specific requirement, balancing is done in two quality categories according to DIN IS0 1940.

Non-operating bending moment

The deflection of the force lines by the inflection angle causes transverse forces and flexural moments on the shaft ends which support the joint or propeller shaft. This phenomenon becomes particularly clear if one imagines the practically useless inflection angle of 90°, in which the entire torque of one drive fork acts as flexural moment in the other. For the shaft ends connected to the propeller shaft this creates a superposition of lateral thrust and flexion which is free of transverse forces. So this means additional load on the bearings of these connected shafts, especially at high angles and torques, a consideration which must be taken into account in the design of the drive.

Choosing the right shaft for an application

Propeller shafts being used for various duties, it is impossible to choose their size and predict their service life with reliable accuracy following just one general rule. Anyway, the familiar failure probability rates for antifriction bearings apply to propeller shafts as well. The size of the propeller shaft should be chosen so that its maximum momentary torque rating, is not smaller than the maximum torque to be transmitted in your application. Additionally parameters like inflection angle, speed, length, operating conditions (kind of drive, temperature, dust etc.) should be considered. Therefore please refer to our technical questionnaire. Our experts will evaluate your informations given in this questionnaire, to find the best choice for your application. If you deem more detailed calcualtions necessary determining lifetime, stability etc. please contact us.

Double jointed propeller shafts

For motor vehicles with front wheel drive should be defined in such a way that the highest short-time torque that can be transmitted is not exceeded in relation to the vehicle's total mass and while maintaining optimum ground adhesion of the tires. Whether differential locks, if any, must been considered or not, depends on the concrete application. The permanent torques of applications with permanent drive must also be considered. The ability of propeller shafts to transmit force is the poorer the larger the angle. Front-wheel drives should therefore not be designed without consulting us.

Installation instructions

To make sure the running quality and precise balancing of the propeller shaft are not impaired, for connecting flanges running at zero-clearance we recommend the centring tolerances and maximum values for radial and axial deviation listed in the table below.

All propeller shafts have an alkaloid-base priming coat; the finish coat can be customized. All anti-corrosion paint should be removed carefully from the propeller shaft flanges before the shaft is installed. Anti-corrosion agent on the propeller mounting flanges reduces frictional adhesion (not with flange yokes with staggered tooth arrangement). On kinematic grounds, make sure that the markings on the length displacement are matching exactly. Otherwise the inner yokes will not be located in one plane and rotation causes vibration and early failure of the drive system components.

Propeller shaft maintenance

The moving parts of a propeller shaft need relubricating at certain intervals, removing used lubricant and foreign matter, if any, and replenishing the lubricant.

Maintenance procedure

Lubricant is supplied to the joints and the sliding member by taper lubricator nipples acc. to DIN 71412 or flat lubricator nipples acc. to DIN 3404. Where the lubricating points on a joint are placed opposite each other, lubricant need only be supplied at one nipple. Make absolutely sure to clean the lubricator nipples before lubrication. The grease reaches four joint bearings through the ducts in the spider. Supply lubricant until lubricant emerges from the seals. The joint bearings of double-jointed propeller shafts are lubricated at lubricators in the bottom of the bearing bushes. Remove old and fill new lubricant according to manufacturer's instructions in the appropriate manual. When supplying lubricant avoid harsh strokes or forceful impact that can damage the seals. The splined shaft connection of the length displacement of propeller shaft requires a controlled supply of lubricant in order to avoid high hydraulic forces that impair the axial movement. Rilsan-coated spline shaft connections require no maintenance.

Lubricant

We recommend the use of lithium soap greases of penetration class 2 with EP additives for European climates, or of nonfreezing grease of the same base for use in temperatures of down to -40°C. Lubricant should never be replenished with a grade of a different soap base.

Maintenance schedule

Maintenance intervals for propeller shafts depend mainly on the conditions of the given application; heavy duty or higher than average ambient temperatures, for instance, lead to faster lubricant consumption. Where high-pressure cleaning is used, relubrication becomes necessary. Hostile environments, heavy soiling or exposure to water, necessitate shorter maintenance intervals. The following are recommended lubrication intervals in the interest of a prolonged service life (The values below are valid only for use at normal conditions):

Safety considerations

Rotating shafts create a hazard. The user must therefore strictly adhere to the safety-standards and take suitable precautions, providing e. g. safeguards or covers. When working at the propeller shaft the drive-motor must be shut off. Disassembling, assembling, repair and maintenance should only be performed by qualified personnel. At such work and at the transportation the propeller shafts have to be secured in such a way, that they cannot slip apart and the flanges are fixed preventing damages to the propeller shaft and avoiding the risk of getting hurt.

Storage of propeller shafts

The propeller shafts should be protected against humidity and stored horizontally side by side (not one on the other one) and fixed, so they cannot roll, or vertically and in this case be secured against falling down.

General instructions

Be sure to follow manufacturer’s instructions for installation and repair.

Parts to be installed in universal drives must be in perfect working order and approved for the specific application in hand.

Make sure that propeller shaft locating centres are properly seated and that the flange surfaces are in perfect contact.

The operation ratings must never be exceeded (Md, ß, n).

Do not use high pressure (water, stream, air) for cleaning to prevent damage of the bearings!

Exploded view of propeller shafts