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Construction machinery and utility vehicles can also benefit from a hybrid drive. This has been verified by tests with a diesel-electric excavator.
© Terex Deutschland GmbH
Drives for mobile machinery
Projektinfo 11/2015

The hybrid drive system combines a 160 kW diesel engine with a 120 kW motor generator.
© DEUTZ AG
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Hybrid building machinery

Hybrid drives make construction machinery not only more economical and quieter – the power from the two engines also provides power reserves for special loads. The advantages of combining a combustion engine with an electric drive have been demonstrated by the DEUTZ engine manufacturing company from Cologne using an excavator. In order to realise the full savings potential, the engineers have also closely examined the auxiliary units as part of the Green Industrial Diesel (GRID) project.

The excavator slowly lifts its boom and its upper superstructure, the house, rotates 180 degrees to the rear. The gripper lowers the 1,000-kilogram test weight and then raises it again immediately before rotating back to the starting position. “We are conducting here one of three precisely defined test cycles,” explains Marco Brun, technical project leader for the GRID project at DEUTZ AG. “This enables us to compare the hybrid drive under practical conditions with a conventional system.”

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Unusual operating noises give the game away: an electric motor is rotating the house. This swing drive is also used to brake the rotational movement, whereby it works as a motor generator and converts part of the kinetic energy back into electrical energy. A supercapacitor pack acting as an electrical energy storage unit enables the energy-saving, two-way feeding and generation of electricity. The excavator’s diesel engine only has to compensate for the energy not recovered and the efficiency losses from the electrical components.

The supercapacitor pack is recharged by the motor generator, which is flange-mounted to the excavator’s 160-kW diesel engine. The generator also plays the decisive role for the excavator’s hybrid drive. When considerable force is needed, the motor generator reverses its function and supports the diesel drive as an electric motor, whereby it uses the energy previously stored in the supercap pack. This power boost decisively improves the system dynamics with peak loads. For instance, the torque is provided particularly quickly by the electric motor when there are abrupt load increases in the operating mode. A start-stop function automatically switches off the combustion engine when the excavator is idle. It is then restarted automatically by using the motor generator.

The diesel-electric hybrid

The engineers are testing the new hybrid drive on a TEREX FUCHS MHL350. The 35-tonne machine can reach up to 16 metres with its boom. The recuperative system shows its advantages particularly well when carrying out movements typical of material handlers. If, for example, scrap metal is being loaded, the house rotates back and forth. With conventional models, each braking movement converts kinetic energy into useless heat. The rotational movement is therefore responsible for more than half of the diesel consumption. The savings potential is particularly great here.

The development engineers view the electric swing drive, however, as just one example of the different loads possible using their hybrid system. “It should be possible to transfer the technology to other construction machinery, forklift trucks, aircraft tractors and agricultural vehicles,” says Brun.

The developers are using a DEUTZ diesel engine as the combustion engine, whose auxiliary units and components have been further optimised to achieve economical operation. An electrical generator from Robert Bosch GmbH is connected to the joint drive shaft via a flexible coupling. The hydraulic pump that moves the material handler boom is located on its stator housing. The drive is designed to be compact so that it can be integrated into the excavator’s standard upper superstructure.

Projektinfo 11/2015:
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Addresses

Project management
DEUTZ AG

Validation of the supercap cells
RWTH Aachen, ISEA

Investigation of interference emissions
EMC Test NRW GmbH

Manufacturer of the supercap pack
WIMA GmbH & CO.KG

Support for the risk analysis
TÜV Rheinland AG

Installation and testing of the hybrid drive in the excavator
Terex Germany GmbH & Co KG

Manufacturer of the electric motor and the inverter for the hybrid drive
Robert Bosch GmbH

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