The price may eventually come down, he adds. "As we scale up, the cost will come down. It's more expensive because there are some more higher-precision components, the larger pump is more expensive than the smaller pump—a lot of fundamental things like that," he says.

The 336EH currently is manufactured in Japan, although Cat has plans to expand production to Victoria, Texas. The hybrid excavator may also be produced at Caterpillar's Belgium plant, depending on demand in European markets.

All the excavator's components are made by Caterpillar, with the exception of the hydraulic accumulator tanks, and maintenance of the hybrid components is designed to match up with the normal service intervals of the excavator.

The fuel savings touted by Caterpillar for the 336EH are not attributed solely to the hybrid power system. The excavator also features a larger-displacement hydraulic pump and an electronically controlled hydraulic valve. "The majority of the hybrid is unchanged from the 336E," says Brian Stelbrink, Caterpillar product application specialist. "But the ACS [Adaptive Control System] valve is taking that hydraulic flow and that power and distributing it to each function on the machine more efficiently. We have greater flexibility with this main valve. It allows us to share flow in a new kind of way." The electronically controlled ACS valve has independent metering, allowing it to manage the inflow and outflow of each circuit in the hydraulic system.

"The electronic control system is new. It's been in development for some time, and we're applying it now on the hybrid," says Stelbrink. "That allows the hydraulic pump to react faster—only when it is needed." Stelbrink cites the electronic control system as the main reason the engine is able to spend most its time at a "high idle" of 1,500 rpm.

Caterpillar has at least two other hybrid excavators on the way: the 336FH and the 336DH. Both will sport the same pump as the 336EH. The 336FH will be powered by a Cat 9.3-liter engine that meets Tier 4 Final and European Stage IV emissions standards. The 336DH will have a Cat 9-liter engine and be targeted to global markets that do not mandate Tier 4/Stage IV emissions standards. "Obviously, some markets care more about costs, others less so about emissions," says Gray.

Meanwhile, the non-hybrid 336E will continue to be available; Caterpillar has no plans to phase it out. "We want the customer to have that option, but we see the hydraulic hybrid as a complete system, not just an add-on," says Gray.