627 Carl Weiss constant velocity joint

A successful constant velocity joint was initially invented by Carl W. Weiss of New York, USA, and was patented in 1925. The Bendix Products Corporation then adopted the Weiss constant velocity principle, developed it and now manufacture this design of joint (Fig. 6.38).

Joint construction and description With this type of time constant velocity joint, double prong (arm) yokes are mounted on the ends of the two shafts transmitting the drive (Fig. 6.37). Ground inside each prong member are four either curved or straight ball track grooves (Fig. 6.39). Each yoke arm of one member is assembled inbetween the prong of the other member and four balls located in adjacent grooved tracks transmit the drive from one yoke member to the other. The intersection of each matching pair of grooves maintains the balls in a bisecting plane created between the two shafts, even when one shaft is inclined to the other (Fig. 6.40). Depending upon application, some joint models have a fifth centralizing ball inbetween the two yokes while the other versions, usually with straight ball tracks, do not have the central ball so that the joint can accommodate a degree of axial plunge, especially if, as is claimed, the balls roll rather than slide.

Carl Weiss constant velocity principle (Fig. 6.41) Consider the geometric construction of the upper half of the joint (Fig. 6.41) with ball track

Dri^e Sail bau track (four)

Dri^e Sail bau track (four)

Constant Velocity Joint

Centra ball

Fig. 6.38 Pictorial view of Bendix Weiss constant velocity type joint

Centra ball

Fig. 6.38 Pictorial view of Bendix Weiss constant velocity type joint curvatures on the left and right hand yokes to be represented by circular arcs with radii (r) and centres of curvature L and R on their respective shaft axes when both shafts are in line. The centre of the joint is marked by point O and the intersection of both the ball track arc centres occurs at point P. Triangle LOP equals triangle R O P with sides L P and R P being equal to the radius of curvature. The offset of the centres of track curvature from the joint centre are L O and R O, therefore sides L P and R P are also equal. Now, angles LOP and

R O P are two right angles and their sum of 90° + 90° is equal to the angle LOR, that is 180°, so that point P lies on a perpendicular plane which intersects the centre of the joint. This plane is known as the median or homokinetic plane.

If the right hand shaft is now swivelled to a working angle its new centre of track curvature will be R' and the intersection point of both yoke ball track curvatures is now P' (Fig. 6.41). Therefore triangle LOP' and R O P' are equal because both share the same bisecting plane of the left and right hand shafts. Thus it can be seen that sides L P' and R P' are also equal to the track radius of curvature r and that the offset of the centres of O R' and O R are equal to L O. Consequently, angle L O P' equals angle R' O P' and the sum of the angles LOP' and R' O P' equals angle LOR' of 180 - 0. It therefore follows that angle LOP' equals angle R' O P' which is (180 - 0)/2. Since P' bisects the angle made between the left and right hand shaft axes it must lie on the median (homokinetic) plane.

The ball track curvature intersecting point line projected to the centre of the joint will always be half the working angle 0 made between the two shaft axes and fixes the position of the driving balls. The geometry of the intersecting circular arcs therefore constrains the balls at any instant to be in the median (homokinetic) plane.

Constant Joint

Shaft shank

Fig. 6.39 Side and end views of Carl Weiss type joint

Shaft shank

Fig. 6.39 Side and end views of Carl Weiss type joint

Weiss Joint
Fig. 6.40 Principle of Bendix Weiss constant velocity type joint
Tracta Joints Angle
Fig. 6.41 Geometry of Carl Weiss type joint

6.2.8 Tracta constant velocity joint (Fig. 6.42) The tracta constant velocity joint was invented by Fennille in France and was later manufactured in England by Bendix Ltd.

With this type of joint there are four main components: two outer yoke jaw members and two intermediate semispherical members (Fig. 6.41(a)). Each yoke jaw engages a circular groove machined on the intermediate members. In turn both intermediate members are coupled together by a swivel tongue (spigot joint) and grooved ball (slotted joint).

In some ways these joints are very similar in action to a double Hooke's type constant velocity joint.

Relative motion between the outer jaw yokes and the intermediate spherical members is via the yoke jaw fitting into circular grooves formed in each intermediate member. Relative movement between adjacent intermediate members is provided by a double tongue formed on one member slotting into a second circular groove and cut at right angles to the jaw grooves (Fig. 6.42(b)).

When assembled, both the outer yoke jaws are in alignment, but the central tongue and groove part of the joint will be at right angles to them (Fig. 6.43 (a and b)). If the input and output shafts are inclined at some working angle to each other, the driving intermediate member will accelerate and decelerate during each revolution. Owing to the central tongue and groove joint being a quarter of a revolution out of phase with the yoke jaws, the corresponding speed fluctuation of the driven intermediate and output jaw members exactly counteract and neutralize the input half member's speed variation. Thus the output speed changes will be identical to that of the input drive.

Relative motion between members of this type of joint is not of a rolling nature but one of sliding. Therefore friction losses will be slightly higher than for couplings which incorporate intermediate ball members, but the large flat rubbing surfaces in contact enables large torque loads to be transmitted. The size of these joints are fairly large compared to other types of constant velocity joint arrangements but it is claimed that these joints provide constant velocity rotation at angles up to 50°. A tracta joint incorporated in a rigid front wheel drive axle is shown in Fig. 6.42(c and d).

6.2.9 Tripot universal joint (Fig. 6.43) Instead of having six or four ball constant velocity joints, a low cost semi-constant velocity joint providing axial movement and having only three bearing contact points has been developed. This joint is used at the inner final drive end of a driving shaft of independent suspension as it not only accommodates continuous variations in shaft working angles, but also longitudinal length changes both caused by road wheel suspension vertical flexing.

One version of the tripot joint incorporates a three legged spider (tripole) mounted on a splined hub which sits on one end of the drive shaft (Fig. 6.43(a and b)). Each of the spider legs supports a semispherical roller mounted on needle bearings. The final drive stub shaft is integral with the pot housing and inside of this pot are ground roller track grooves into which the tripole rollers are lodged.

In operation, the stub shaft and pot transfers the drive via the grooves, rollers and spider to the output drive shaft.

Constant Velocity Joint
Fig. 6.42 (a-d) Bendix tracta joint

Cylindrical Parallel pot member roller

Cylindrical Parallel pot member roller

Bendix Weiss Joint Cut Section
la) Tripot joint side view

Roller track

Roller track

(b) Tripot joint end view

Fig. 6.43(a and b) Tripot type universal joint

When there is angularity between the final drive stub shaft and drive shaft, the driven shaft and spider will rotate on an inclined axis which intersects the stub shaft axis at some point. If the motion of one roller is followed (Fig. 6.43(a)), it will be seen that when the driven shaft is inclined downwards, when one spider leg is in its lowest position, its rollers will have moved inwards towards the blind end of the pot, but as the spider leg rotates a further 180° and approaches its highest position the roller will have now moved outwards towards the mouth of the pot. Thus as the spider revolves each roller will roll to and fro in its deep groove track within the pot. At the same time that the rollers move along their grooves, the rollers also slide radially back and forth over the needle bearings to take up the extended roller distance from the centre of rotation as the angularity between the shafts becomes greater and vice versa as the angle between the shafts decreases.

Because the rollers are attached to the driven shaft through the rigid spider, the point of contact between the three rollers and their corresponding grooves do not produce a plane which bisects the angle between the driving and driven shafts. Therefore this coupling is not a true constant velocity joint.

6.2.10 Tripronged universal joint (Fig. 6.44) Another version of the three point contact universal joint consists of a triple prong input member (Fig. 6.45(b)) forming an integral part of the drive shaft and an output stub axle cup member inside which a tripole spider is located Fig. 6.44(a). Three holes are drilled in the circumference of the cup member to accommodate the ends of the spider legs, these being rigidly attached by welds (Fig. 6.44(a and c)). Mounted over each leg is a roller spherical ring which is free to both revolve and slide.

(c) Tripronged joint - end view

Fig. 6.44(a-c) Tripronged type universal joint

(c) Tripronged joint - end view

Fig. 6.44(a-c) Tripronged type universal joint

When assembled, the input member prongs are located in between adjacent spider legs and the roller aligns the drive and driven joint members by lodging them in the grooved tracks machined on each side of the three projecting prongs (Fig. 6.44(c)).

The input driveshaft and pronged member imparts driving torque through the rollers and spider to the output cup and stub axle member. If there is an angle between the drive and driven shafts, then the input drive shaft will swivel according to the angularity of the shafts. Assuming that the drive shaft is inclined downwards (Fig. 6.44(a)), then the prongs in their highest position will have moved furthest out from the engaging roller, but the rollers in their lowest position will be in their deepest position along the supporting tracks of the input member.

As the shaft rotates, each roller supported and restrained by adjacent prong tracks will move radially back and forth along their respective legs to accommodate the orbiting path made by the rollers about the output stub axle axis. Because the distance of each roller from the centre of rotation varies from a maximum to a minimum during one revolution, each spider leg will produce an acceleration and deceleration over the same period.

This type of joint does not provide true constant velocity characteristics with shaft angularity since the roller plane does not exactly bisect the angle made between the drive and driven shaft, but the joint is tolerant to longitudinal plunge of the drive shaft.

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