In June 2008, Komatsu launched the PC200-8 hybrid crawler excavator for release exclusively in the Japanese market. At Intermat, it was announced that the hybrid would be available to the rest of the world. The hybrid system consists of an electric motor to turn the upper structure, a generator, capacitor bank, and a diesel engine. With these four components working together, fuel savings are around 25% more than a standard model.
Thirty of the hybrids have been sold, and several were monitored for actual results in the workplace. Consumption reductions from 30% to 41% were achieved, with locations varying from waste disposal to civil engineering to sludge disposal. The nature of the work impacted the consumption levels, with sludge disposal being the most improved as it required more upper structure turning.
Experimenting with the first hybrid excavator began on the flagship of the Komatsu line, the 20-t (22-ton) model in the Dash 8 range. All components of the hybrid system are designed and manufactured in-house by Komatsu, with the exception of the capacitors.
The hybrid system begins with a diesel engine to power the generator. This generator powers the electric turntable motor. As the turntable slows, energy is collected in the capacitor, from where it is sent back to the generator to add high-torque electric power for assistance as the diesel accelerates. This feature enables the diesel to be kept at a lower rpm range and, therefore, reduce fuel use.
Upper structures of tracked excavators are usually hydraulic, but as the swing cycle is repetitive and involves significant forces, having an electric motor that can power the turntable and also collect the energy as it slows is doubly beneficial.
Capacitors are used rather than batteries as short, high-power applications are regular during the work cycle of an excavator, and long-lasting continuous power would be better served by batteries.
As a comparison, Komatsu cites the differences between hybrid construction equipment and hybrid road vehicles. Whereas cars require a great deal of energy to initiate movement but can then run at a relatively stable rpm, construction equipment is faced with varying intensities of demands, and thus the lower power from an automotive battery-hybrid system, based on a chemical reaction, would not be suitable. Capacitors can instantly store and discharge energy in bursts of power, as and when the machine requires it.