How is the crane sector embracing hybrid power systems? IC reports.

Consideration of the environmental impact of cranes, both through their life and from the manufacturing process, is an increasingly important issue. One example is the hybrid power system with lower exhaust emissions. Euan Youdale reports.

Liebherr has launched what it describes as the industry's first hydraulic hybrid drive for mobile harbour cranes. Pactronic is an energy storage device where an hydraulic accumulator supplements the hydraulic pump in delivering power to the system. It is a pressure storage reservoir containing gas and hydraulic fluid. Energy is stored in the compressed gas and released on demand.

Pactronic is also a power booster. Hoisting as well as lowering speeds are increased substantially, says the company, without the need for a bigger diesel engine with more output. In addition, fuel consumption is reduced, achieved using the reverse energy and surplus power in the system.

"We believe Pactronic is one of the most important innovations we've come up with to date," says Dr. Klaus Schneider, director drive systems at Liebherr.

Dutch manufacturer Spierings launched a hybrid mobile folding crane at the Bauma 2010 exhibition in April. The SK387-AT3 Ecodrive, nicknamed City Boy, has a battery-electric drive for road travel. It is described a true hybrid as there is no direct mechanical connection between the engine and the wheels.

Onboard is a diesel generator that charges the chassis-mounted traction batteries that power an electric motor on one of the crane's three axles. The batteries can also be charged from 400 Volt AC site power. regenerative braking saves energy by using energy generated by braking to charge the batteries.

Stable power

Also at Bauma, ZF unveiled its Ergopower hybrid and cPower transmissions. ZF cPower is a continuously variable transmission using planetary gears that obviates the need for a traditional gearbox and transmission components. The system offers the advantages of a mechanical design and of an hydrostatic drive. ZF claims the result is a 30% reduction in fuel consumption and a 20% increase in efficiency.

Spokesman Alexander Eisner said, "A trend towards lower engine speeds and the demand for engine stabilisation - whereby the engine runs at a constant speed - are the future challenges for OEMs. ZF's continuously variable cPower meets both criteria."

The Ergopower hybrid system is the next step in ZF's efficiency package. Matching components, for example, the Ergopower transmission, Multitrac axles and software, ZF has integrated an electric motor and lithium-ion battery into the existing transmission, the result of which is lower exhaust emissions, reduced fuel consumption and increased productivity.

Eisner said, "The ZF Ergopower hybrid works as a parallel hybrid with an efficient electric motor, providing up to 120 kW of power. Interaction between the electric motor and combustion engine is matched to avoid situations which would otherwise lead to poor efficiency and increased emissions.

"This system offers reduced fuel consumption and the opportunity for simplified exhaust after treatment. Because the system captures braking energy, we believe OEMs will be able to consider down-sizing their choice of combustion engine."

Number one

Another consideration in the mobile crane industry is whether to use one engine or two. An example comes with the two latest 6-axle all terrains from Manitowoc: the 300 tonne capacity GMK6300L and 400 tonne GMK6400.

A big difference between the two new cranes is that the larger one is a single engine design with idle reduction package instead of the more conventional two engines in this class as used in the GMK6300L and competing models. Both use the carrier mounted 405 kW Mercedes OM 502 LA Euromot IIIB V8 diesel.

Advantages of the single engine concept include a lower centre of gravity and lower overall weight. Manitowoc has calculated that, in daily work, using the larger carrier engine to power crane operations instead of a smaller dedicated engine in the upper offers better fuel consumption.

A comparison between the OM 502 carrier engine and the OM 906 for crane operation shows the larger engine consuming 28 litres an hour - one litre less than the smaller engine. It is only at low engine speed where the crane is running but no crane functions are operating and power is only needed to run air conditioning or heating. In this situation the main engine can shut down and a small auxiliary diesel generator can take over.