“Hybrid technology is definitely a key enabler to improve overall vehicle efficiency,” Tom Apostolos, President of Ricardo, recently told SOHE.
Many off-highway OEMs are evaluating opportunities for hybridization, though Apostolos noted the challenges in making the business case because of low volumes along with diverse models and duty cycles. “Even though a great technical solution may exist, it may be challenging to develop a business case for a bespoke vehicle,” he said.The key is low operating cost coupled with as low an initial cost as possible to get good payback.
He outlined three energy architectures for hybridization: electric, hydraulic, and flywheel. The current adoption of electric technologies (either battery- or ultracap-based) in the off-highway market “may have been influenced by the wide range of electric hybrid technologies developed for on-highway vehicles,” he said. Hydraulics are useful in duty cycles that require high power with low long-term energy storage, such as excavators. For example, Caterpillar recently launched its 336E H hybrid excavator using hydraulic accumulators to store energy while Hyundai has had an ultracap excavator since 2011.
Ricardo predicts the future is in flywheels.
To prove the point, Ricardo developed its HFX (High Efficiency Excavator), a wheeled excavator demonstrator. They showed it at Bauma in mid-April. “We chose an excavator based on earlier investigations that identified it as a prolific consumer of fuel,” said Apostolos. The company claims 10% fuel savings overall, with 30% fuel savings in some duty cycles. They adapted the flywheel technology from earlier demonstration projects in buses and rail cars.
The company makes a point that flywheel energy storage is anything but new, first dating to 8000 BC as used in potter’s wheels. More recently it was used in the 1970s on Lockheed’s Kinetic Energy Wheel and in the 1980s on General Electric’s Flywheel bus. The key to its utility in particular duty cycles, like excavators, is when energy storage is low but peak power is high.
Ricardo innovated the basic flywheel in a number of ways. The flywheel is hermetically sealed in a container, with a sealed-for-life vacuum, transmitting power through a magnetic gear drive. They use high-speed rolling elements with a composite flywheel unit that allows the system to spin up to 60,000 rpm. The vacuum environment means low losses due to air friction. The demonstration system stores 0.25 kW·h and delivers maximum torque of 28 N·m (20.6 lb·ft) as measured at the flywheel. The company noted that is working on three storage units rated at 0.055 kW·h, 0.25 kW·h, and 1.25 kW·h.
Since it uses relatively simple components, Ricardo states the system will be considerably more cost-effective than that of a traditional electrical battery hybrid system, while delivering 80% of the fuel economy. Since it has a 65% lower entry cost, Ricardo feels “the uptake of the system will be high across a number of different vehicle sectors,” according to a company spokesman.