Double Cardan Query

[Bohica]

I'm assuming that the output of the transfer case is parallel to the input of the front diff. Yet the transfer case has a double cardan joint, to allow a wide range of movement. Surely the same wide range of movement occurs at the diff end, with only a standard universal joint. If the axes of the transfer case out put and diff input are parallel that the angle changes at both ends will be identical. So why a double cardan only at one end? What am I missing?

Thanks

Julian

[PhilipA]

IMHO the double Cardan is primarily to decrease vibration.
A Hooke joint does not travel at a constant speed , it slows and quickens 8? times on each revolution.
2 Hooke joints means twice the speed change =vibration.

The double Cardan reduces the speed differences particularly at larger angles.
Regards Philip A

[mattims]

The output of the transfer case is near to vertical and the input to the diff is not that near (it is closer to inline with the shaft, but also not exact) so the double joint is to remove vibrations from angle mismatch rather than allow extra movement.

[Jazzman]

As far as i understand, it is a double cardan joint because the shaft is short therefore the angle is greater than, say a Toyota Land Cruiser. With 2 uni joints the angle is split between both joints, each taking half.

Best analogy I can think of is using 2X 45 degree drain pipe fittings to make a 90 degree bend.

This then deduces the vibrations and stress on the uni's because they don't have to bend / twist as far on their vertical plane.

[bee utey]

The reason that a double cardan joint works to reduce vibration is because the two joints almost exactly cancel out each others speed variations.

Link with animated pictures:

3D CAD Model Collection | GrabCAD Community Library (https://grabcad.com/library/double-cardan-joint-1)

[DiscoClax]

Yep, Bee Utey is spot on. A double cardan is classified as a CV (Constant Velocity) joint because of this.

[Jazzman]

I'm assuming that the output of the transfer case is parallel to the input of the front diff. Yet the transfer case has a double cardan joint, to allow a wide range of movement. Surely the same wide range of movement occurs at the diff end, with only a standard universal joint. If the axes of the transfer case out put and diff input are parallel that the angle changes at both ends will be identical. So why a double cardan only at one end? What am I missing?

Thanks

Julian

They're actually not parallel. Without lift the front diff flange it 90 degrees to the ground, but the front output flange on the transfer case is pointing to the sky slightly. If you've got a broken rear rubber mount it is even worse.

Once lifted the front diff flange points towards the TC but the front output flange is still in the same position. Very over exaggerated the flanges look like this after a lift DIFF \/ TC. Before a lift Diff |/ TC. Not || as you would expect.