Axle "Equalizer"

It's just what the name implies. It equalizes the load between each axle. Otherwise, even the slightest change in attitude of the trailer would move the load towards one of the axles. The equalizers also help allow the axles to "walk" over bumps.

Many car trailers don't have equalizers, making it extremely important to tow it perfectly level. And those also suck once you leave pavement, because you feel every bump twice.

As name implies.......it equalizes the 'dynamic loading' on multiple axles

scroll down to equalizer.
https://www.etrailer.com/faq-double-eye-trailer-suspension-review.aspx

http://www.dexteraxle.com/equalizer_comparison

Jayco uses a mor-ryde

http://www.morryde.com/uploads/downloads/1415135859-CRE%20Owners%20Manual.pdf