Another pic of concept
Here
Also , BOSE produces a system as well ...
Link ... very small scale ... but their system not only works passively to recover wasted suspension dissipated energy , but AFAIK it also works dynamically which consumes power but allows for better suspension than a conventional passive system... I think their tiny niche market is for the use more energy for luxury side.
A Paper on the concept ...
Link
Another Write up Article on Concept ...
Link