USA: Ford boffins nix A/C click
Magnetorhelogical material (MR material), the 'official' lab name can behave as a free-flowing liquid, a paste-like solid, or anything in between, switching properties instantly when a magnetic field is applied.
Ford is said to be experimenting with the use of MR material in air-conditioning compressors as a way to subdue the audible clicking that occurs when the clutch engages and disengages. The MR material allows the clutch to gradually engage, providing a smoother, less noisy contact or "soft start."
When the clutch disengages, the material reverts from the solid "locked-up"
state to a fluid to let the clutch slip out of contact. This soft engaging and
disengaging of the clutch also makes power surges from the engine less noticeable,
a condition typically felt in vehicles equipped with small displacement engines
and air conditioning.