Hybrid is a slippery word. By one definition, anything of mixed origin or composition is a hybrid: thus, we have hybrid roses and hybrid languages. A more narrow definition has hybrids as single functioning units that juxtapose different technologies. That definition makes hybrids of decades-old hydrostatic and diesel/electric drive systems—since they juxtapose mechanical with hydraulic or electric technology—but these systems seldom are so classified. When considering the innovative energy-use systems being applied today in heavy equipment and trucks, then, perhaps “hybrid” definitions need a second look.
The most precise definition we encountered is that from Caterpillar: A hybrid is “a machine equipped with a device to collect, store and release energy during operation.”
By that definition, a number of machines and trucks with innovative energy-use technology would qualify as hybrids. A few machines, however, with technology just as innovative, would be ruled out on technicalities—the Cat D7E crawler dozer, for instance, because its distinctive electrical/mechanical power train neither collects, stores nor releases stored energy, and several wheel loaders—the Cat 966K XE, Deere 644K Hybrid, and Deere 944K—which collect and use energy that otherwise would be wasted, but do not store it.