[fordem]

Many years ago I came across the term birfield and was quite puzzled by it - as far as I can tell - a birfield joint is a CV joint (specifically a rzeppa joint) as used in a live axle - does any one agree/disagree with this?

I came across the term birfield in connection with birfield rings - a metal ring being press fitted to the outer end of the CV joint to strengthen it - and this leads to me next question - can a birfield ring be made/fitted to a CV joint as used on an IFS axle like a Vitara/Grand Vitara.

A little off topic - but not entirely - I've noticed that some live axles, specifically those used on US pickups don't use birfields, they have a single universal joint which I have always been told needs to be used in pairs to maintain constant angular velocity, which is why a birfield needs to be used - so how do these axles with a single UJ work?

[want33s]

As far as I know, the difference is a Birfield joint uses balls and a CV joint uses rollers albeit spherical. This isn't 100% though.

A ring could be fitted to a GV CV but they I doubt there's much point as they don't usually break the case, more often it's the internal spline that chews out when the 'star' gear cracks.

Dana axles just use a uni joint and they work fine.

[Brenno]

Also, uni joints in axles turn a lot slower than uni joints on driveshafts.

[fordem]

want33s wrote:

As far as I know, the difference is a Birfield joint uses balls and a CV joint uses rollers albeit spherical. This isn't 100% though.

There are different types of CV joints - I grew up with the British Leyland Mini & 1100/1300, on which the outer CVs use balls, in what is known as a rzeppa joint, in my experience, most outer joints are rzeppa (the only other outer joint I've disassembled was a double cardan), inner seem to use a tripod or tulip with rollers to allow for changes in length (or plunge), and I could be wrong, but I believe the GV outer is a rzeppa, and the inner is a modified rzeppa with slots in the outer cup to allow for "plunge".

Quote:

Dana axles just use a uni joint and they work fine.

No argument there - the question is why are we told a constant velocity joint is needed - if that is correct the dana should not work.

[Zook_Fan]

My understanding is single uni joint axles work because the displacement of ends is only in one plane (unless there is a small amount of caster/camber). A driveshaft has displacement in the x and y axis if you were looking from the top of the chassis, combined with the fixed yokes you cannot just use one uni joint.

CV's, or constant velocity joints, allow a much smoother transition of power. No matter what the angle is they are still generally smooth however they loose strength the more they are turned. Uni's are susceptible to notching and being hard to turn when you have a large range of steering, they can bind. They work, and can be much stronger than a CV joint but you won't find them in cars built for comfort.

Quote:

The term "birfield" as referencing our beloved cv joints comes from the the "Birfield Group".
The "Birfield Group" of companies (UK) manufactured a variety of drivetrain products (primarily propeller shafts) in the fist half of the 20th century. Their companies included Hardy Spicer.
Hardy Spicer--formed when Dana Spicer (US) purchased ownership in E.J. Hardy and company (UK)--purchased the rights (in 1956) to the constant velocity joint designed by Alfred H. Rzeppa in the 1930's.
In 1963, NTN (Japan) licensed manufacture of the Rzeppa style cv joint from Hardy Spicer (a Birfield Group company).

For more information on "Birfields" search the term "Birfield-Rzeppa".

[fordem]

Zook_Fan wrote:

My understanding is single uni joint axles work because the displacement of ends is only in one plane (unless there is a small amount of caster/camber).

One plane or two planes makes no difference to the joint - take a piece of wire and try this yourself - rotate 45* horizontal and then 45* vertical - total angular displacement will be 45*.

Quote:

A driveshaft has displacement in the x and y axis if you were looking from the top of the chassis, combined with the fixed yokes you cannot just use one uni joint.

I'm not quite certain where you're coming from here - assuming you're referring to the drive shaft on a front engined, rear wheel drive car, looking from above, there will be movement in neither x nor y axes, only in the z axis (up/down), looking from the side the movement will be in the y axis, and there have been driveshaft designs that only use a single joint at the transmission end. Research Hotchkiss & torque tube - the following quote is taken from the Wikipedia article on torque tubes and illustrates my point perfectly.

Wikipedia wrote:

In most applications the drive shaft uses a single universal joint which has the disadvantage that it causes speed fluctuations in the driveshaft when the shaft is not straight. The Hotchkiss drive uses two universal joints which has the effect of canceling the speed fluctuations and gives a constant speed even when the shaft is no longer straight

This second quote comes from the article on Hotchkiss drives

Wikipedia wrote:

The differentiating characteristic of the Hotchkiss drive is the fact that it uses universal joints at both ends of the driveshaft, which is not enclosed. The use of two universal joints, properly phased and with parallel alignment of the drive and driven shafts, allows the use of simple cross-type universals. (In a torque-tube arrangement only a single universal is used at the end of the transmission tailshaft, and this universal should be a constant velocity joint.)

Quote:

The term "birfield" as referencing our beloved cv joints comes from the the "Birfield Group".
...
For more information on "Birfields" search the term "Birfield-Rzeppa".

Thanks for pointing that out - it promises to keep me occupied for many hours.

[Zook_Fan]

fordem wrote:

Zook_Fan wrote:

My understanding is single uni joint axles work because the displacement of ends is only in one plane (unless there is a small amount of caster/camber).

One plane or two planes makes no difference to the joint - take a piece of wire and try this yourself - rotate 45* horizontal and then 45* vertical - total angular displacement will be 45*.

Yes. But how many uni joints can handle a displacement of 45*? Not very many, in fact to get 45*+ steering with those joints gets very expensive for the guys building the axles to suit. If you care to waste some more time:
Customed machined axles here: http://www.branikmotorsports.com/axle.htm
New axles here: http://www.spidertrax.com/Ultimate-300M-Axle-Shafts

I know that was an example, I'll explain myself better soon.

fordem wrote:

Quote:

A driveshaft has displacement in the x and y axis if you were looking from the top of the chassis, combined with the fixed yokes you cannot just use one uni joint.

I'm not quite certain where you're coming from here - assuming you're referring to the drive shaft on a front engined, rear wheel drive car, looking from above, there will be movement in neither x nor y axes, only in the z axis (up/down), looking from the side the movement will be in the y axis, and there have been driveshaft designs that only use a single joint at the transmission end.

They will move in the x and y axis unless the transfer is solid mounted. It will just be torquing of the case so it will be minor and that's not really what I meant. Looking from the top of a car the output of the transfer and the pinion yoke are not always directly in line. I'm doubting myself right now, but from memory I believe there will be an offset difference. Again, the shaft doesn't know what planes it is bending in but it can only bend so far. So with only a single you will be getting to a critical angle a lot sooner with less articulation of the suspension.

A constant velocity joint is just that, it is constant. A uni joint is not constant, because it is not balanced it causes irregular speed of the shaft. By adding a second uni joint, correctly in phase, the outputs net angle of rotation is zero. In a single uni joint axle you will get vibration from the front end of the car unless driving straight ahead.

fordem wrote:

Research Hotchkiss & torque tube - the following quote is taken from the Wikipedia article on torque tubes and illustrates my point perfectly.

Wikipedia wrote:

In most applications the drive shaft uses a single universal joint which has the disadvantage that it causes speed fluctuations in the driveshaft when the shaft is not straight. The Hotchkiss drive uses two universal joints which has the effect of canceling the speed fluctuations and gives a constant speed even when the shaft is no longer straight

This second quote comes from the article on Hotchkiss drives

Wikipedia wrote:

The differentiating characteristic of the Hotchkiss drive is the fact that it uses universal joints at both ends of the driveshaft, which is not enclosed. The use of two universal joints, properly phased and with parallel alignment of the drive and driven shafts, allows the use of simple cross-type universals. (In a torque-tube arrangement only a single universal is used at the end of the transmission tailshaft, and this universal should be a constant velocity joint.)

I'm familiar with the torque tube arrangement. In the cars that have used them the shaft has been ran through a rubber donut and the single unit joint goes through a torque tube rubber. These two rubber mounts help to dampen the vibrations caused by the single joint however they cannot stop the inevitable change in angular velocity.

fordem wrote:

Quote:

The term "birfield" as referencing our beloved cv joints comes from the the "Birfield Group".
...
For more information on "Birfields" search the term "Birfield-Rzeppa".

Thanks for pointing that out - it promises to keep me occupied for many hours.

No worries, keeping me occupied too . In answer to your original question, single uni joint axles work because they still provide angular motion to the wheels. They do cause vibration and they are not as smooth as CV's but they work.