Thread: Thompson Coupling

looks weird,,,

...looks beautiful

(Supposed to offer much less resistance - saving energy - when operating at angles compared to a conventional uni or C.V. joint)

...I think

It will be interesting to see how they go in practice - compared to a conventional cross & bearing or Rzeppa joint they are complex and expensive - I have never been able to work out exactly how they work! And while Rzeppa joints are not able to be serviced, the conventional cross and bearing type can be serviced cheaply, and has a very long history of successful use , nearly 100 years.

It might be worth noting that although Rzeppa invented his joint in 1928, it did not appear in a car until the Mini in 1958, since then having gradually become more or less standard for all front and four wheel drive cars. Previous front or four wheel drive cars either used a conventional cross and bearing and don't worry about constant velocity (Landrover 1951 - 1983, BSA, Cord, FWD and others), used double cardan joints (Citroen), or used Tracta joints, invented by Gregoire in the early twenties (Landrover 1948-1951, Willys, Panhard and others) or occasionally other types of joint. As with any established design, the Rzeppa CV joint will be very hard to displace, even if the Thompson coupling is superior - the existing one is "good enough" and is being mass produced.

John

I remeber the review of these from i think it was beyond 2000, aparently they were eventually going to replace the CV and the Uni...

till the penny pinchers got in on the act....


why have better when you can have cheaper items with bigger profit margins?


when these guys get intouch with maxi and make those things to go as off shelf items for landrovers in the various spline counts and lengths I'll be buying.

How do these compare to the Cornay joint though?

Product Description Cornay® 50° Constant Velocity Joints are designed to provide a high-angle, high-speed, self-supported connection between a driving component and a driven component. Cornay® CV Joints can operate at angles up to 50° and provide reliable transfer of power in extreme operating conditions.

Applications Cornay® 50°CV Joints are adaptable to a wide variety of off-highway and on-highway applications including PTO applications, particularly those that require combinations of high angle, speed and torque.

Performance Advantages The high angle, speed and torque capability provide a high degree of design flexibility for extreme power train applications. Drive Technologies also provides engineering services to help you meet your vehicle’s specific requirements.

Originally Posted by Slunnie

How do these compare to the Cornay joint though?

That is simply a particular implementation of a "double cardan joint" These are used, for example, at the rear of the front prop shaft on Rangerovers, Discoveries and Stage 1s, as well as most Toyota and Nissan 4x4s, and were used in front half axles of Citroens from 1936 to 1975.

Prompted by that picture though, I have had another look at the Thompson coupling, and I think that it is actually a double cardan joint with one of the joints placed inside the other! This gets around the principal drawback of the double cardan (apart from cost), that it is too bulky, particularly lengthwise.

John

Ah ok. This is an axle type CV rather than something like the Cornay which is a tailshaft type CV/DC joint.

Originally Posted by JDNSW

That is simply a particular implementation of a "double cardan joint" These are used, for example, at the rear of the front prop shaft on Rangerovers, Discoveries and Stage 1s, as well as most Toyota and Nissan 4x4s, and were used in front half axles of Citroens from 1936 to 1975.

Prompted by that picture though, I have had another look at the Thompson coupling, and I think that it is actually a double cardan joint with one of the joints placed inside the other! This gets around the principal drawback of the double cardan (apart from cost), that it is too bulky, particularly lengthwise.

John

Good call John.

The Thompson Coupling is certainly amongst the most important inventions since the advent of the internal combustion engine. It is the world's first and only, practical, constant velocity joint to have no load bearing sliding surfaces.
Shaft couplings are essential to our mechanised era. Amazing as it may seem, although mankind has landed men on the moon and done so many other wondrous things he has not been capable of efficiently transmiting power from one shaft to another at constant velocity. This is an invention which has been actively sought for about 400 years when Sir Robert Hooke made the first known attempt to construct a constant velocity coupling.

• The Thompson Coupling is as essential to our mechanised age as the screw, the crank, the lever and piston
• The Thompson Coupling is the world's first and only Constant Velocity Joint which:
• Has all loads carried by roller bearings
• Has no sliding or skidding surfaces whatsoever
• Can tolerate axial and radial loads without degradation
• Has no torque limitation, constructed to any torque level
• Does not require special lubrication
• Does not require a dust boot
• No wearing components except replaceable bearings and trunnions
• Is suitable for automotive tail or propeller shaft applications
• Is a true Constant Velocity Coupling as distinct from a cv joint
• Is less bulky than a double coupling or double Cardan joint.

The Thompson Coupling is essentially two Cardan joints assembled coaxially where the cruciform-equivalent members of each are connected to one another by trunnions and bearings which are constrained to continuously lie on the homokinetic plane of the joint.

The constraining means which constrains the said trunnions and bearings consists of a two segment spherical four bar linkage or spherical draglink. One end of the draglink is attached to a trunnion on an extension to the input shaft while the second end of the draglink is connected to a removable pin forming a trunnion on the inside of the yoke of the output shaft. Each arm or bar of the draglink continuously forms a great circle arc centered upon the axis of the joint. The central axis of the draglink is located on a trunnion in the middle of a "C" shaped member, the ends of the "C" shaped member are located on the extended trunnions which connect the two Cardan joints.
With operation of the joint, the central axis of the draglink and therefore the trunnion in the center of the "C" member, continuously bisects the included acute angle between the extended axis of the input and output shafts and therefore continuously lies on the axis of the homokinetic plane of the joint.

Consequently the axis of the trunnions which connect the inner and outer Cardan joints are constrained to continuously lie on the homokinetic plane of the joint. (Note:- The homokinetic plane is that plane which is perpendicular to the plane of the axis of the input and output shafts and which bisects the obtuse angle between the axis of the input and output shafts.)
As is well known, four bar linkage mechanisms are structurally excellent and this remains true in spherical form.
In operation the component parts of the coupling remain balanced about the three rotational axis of the joint namely the input shaft axis, the output shaft axis and the axis of the homokinetic plane.
In mass production each and every component of the Thompson Coupling can be produced by forging and/or casting with the only further requirement being to drill and machine the bearing journals, holes and circlip grooves.
No dedicated machinery is required and there is no complex machining at all.
Bearings for most applications are stock and assembly is very simple.
For one-off project applications, manufacture is simple and within the capability of any machine shop. No specialist machinery is required as is the case with Rzeppa type joints.

The Thompson Coupling has essentially the same construction as a normal Cardan joint but does not suffer the dynamic loads due to fluctuating angular velocity of intermediate shafts and load as is the case where Cardan joints are used.
As a result, the Thompson Coupling should have a life exceeding an ordinary Cardan joint. It stands to sense, and our testing will prove it. There is no untried technology in the Thompson Coupling. It is essentially identical to two Cardan joints in its torque transmission.
The components and the moving components in the constraining mechanism are tried and true roller bearings. There are no mysteries or unknowns.
A Thompson Coupling can be disassembled with a pair of circlip pliers and the bearings replaced with a minimum of expertise and downtime.

The Thompson Coupling is very compact and may be over-engineered to increase reliability without adding substantially to bulk and weight.

It is obvious that use of the Thompson Coupling in lieu of Cardan Joints will eliminate a large source of vibration in many machines and automotive applications.