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Flybrid's latest 600-series flywheel energy recovery family of modules is described as "compact and cost-effective" (image: Flybrid).

Using power dense flywheel hybrid technology to cut fuel consumption of OH equipment

Flywheel hybrid system developer Flybrid is creating a family of flywheel modules designed to enhance productivity and cut operating costs of off-highway vehicles and construction equipment. Designed to supplement the main powertrain, the modules can be connected hydraulically, mechanically or electrically.

Flybrid, part of the Torotrak Group, has developed its KERS (Kinetic Energy Recovery System) for applications ranging from F1 race cars to buses. But now it is widening its technology spectrum.

Richard Dunne, Flybrid’s Business Development Manager, said: “Flywheels are an incredibly power-dense method of storing and releasing energy and a flywheel hybrid is a compact and cost-effective way to hybridize a machine.”

The initial new family of flywheel modules is designated 600 Series and spans an energy storage range from 150kJ to 600kJ, with the first production example, the H-380, able to store up to 380kJ and integrate with a machine’s hydraulic system. It would be suitable for excavators weighing 20 to 45 tonnes, for example, or wheeled loads in the 75 kW to 225 kW power range.

Dunne explained that the H-380 system harvests both kinetic and potential energy that would otherwise be wasted during the machine’s operating cycle and releases it at the required power during the next cycle: “Examples include raising and lowering the boom of an excavator or the mast on a reach stacker; slewing on an excavator or shuttling between forward and reverse with a loader. It delivers up to 210 kW of additional power to the machine to significantly improve productivity.”

He sayid that Flybrid demonstrated the system in a vehicle program using its 210-kW flywheel hybrid in a typical sub-130 kW (engine power), 22 tonne excavator.

Meaningful consumption reductions, rigorous validation

Previous Flybrid customer applications have demonstrated a fuel-consumption reduction of 15% when used to recover energy in a mobile machine—and typical fuel-consumption reduction in load-leveling applications is 30%, added Dunne.

In the example of an excavator, boom lowering is typically controlled by throttling the return of flow from the boom cylinder, wasting the available energy by turning it to heat.

When a hydraulically-connected Flybrid system is added to the excavator, this flow is diverted to a variable-displacement pump, which in turn charges the flywheel. Due to the variable control of the pump, the flywheel can be charged regardless of the available pressure level or the state-of-charge of the flywheel (unlike an accumulator), explained Dunne: “To release the energy when raising the boom, fluid is returned from the flywheel-driven pump by controlling the pump swash exactly at the pressure demanded. Again, the pressure that can be supplied is independent of the energy remaining in the flywheel.”

He says he fully understands that plant operators may be cautious—even skeptical—when presented with an all-new technology in a business world where reliability, robustness and quality are absolute “musts” to avoid delays caused by malfunctioning equipment.

So over the last 18 months, Flybrid has focused its resources on productionizing the H-380 system, working with its off-highway partners to complete an extensive validation program.

Dunne detailed part of the process: “Flybrid has the capability to run full flywheel hybrid systems and critical sub-systems on test rigs at real-world operating temperatures. As part of the rig-based validation testing, full-life durability testing has been completed. Furthermore, this validation program included operating the H-380 system in a customer’s machine in a quarry. With this in-machine testing, Flybrid was able to show that its rig-based full- and sub-system validation was an accurate representation of real-world conditions. As part of this validation program, we also completed extreme inclination testing at operating angles beyond the capabilities of a quarry machine.”

Previously, Flybrid developed hybrid systems capable of reliably delivering more than 1000 kW of additional power in extreme environments both on- and off-road, stated Dunne: “So we know our H-380 product, that delivers 210 kW of additional power, sits well within our comfortable operating range. The proven reliability, coupled with the high power density of the system, makes it an attractive option for operators.”

He explained that in addition to recovering waste energy, the flywheel hybrid system can be used to load-level the engine. By “pre-charging” the flywheel, the energy can be used to smooth the peak loading on the engine, which in turn enables engine downsizing or downspeeding to reduce fuel consumption without impairing functionality.

The Flybrid system is integrated with the main machine control system, designed to provide the same smooth and predictable operability as on the original machine. The control system of the flywheel hybrid can be configured to select the optimum source of energy from multiple sources within the machine’s hydraulic control system and so will harvest the maximum amount of energy during an operation cycle.

Flybrid is working with leading off-highway equipment manufacturers to implement flywheel hybrid systems in a variety of machines and applications. Apart from the production-ready H-380 Flybrid, the UK Advanced Propulsion Centre (APC) recently announced a project involving Turner Powertrain Systems Ltd. (a wholly-owned subsidiary of Caterpillar Inc.) and Flybrid. During the project an additional Flybrid product will be developed to a production-ready status for installation in a range of Caterpillar’s off-highway machines.

“The power dense Flybrid Flywheel Hybrid System is well-matched to the requirements of heavy-duty applications,” added Dunne. “It is designed for over 20,000 hours’ life in extreme operating conditions.”

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