The R 9XX concept crawler excavator that Liebherr unveiled earlier this year uses energy recuperation techniques that it says will improve the economy and sustainability of construction machines.
Based on the machine structure and system architecture of a 40-t (44-ton) excavator, the R 9XX is powered by a Liebherr engine that, with a power output of 160 kW (218 hp), is much smaller than the engines normally encountered in that service-weight category. The benefits are decreased fuel consumption and emissions with additional performance from the electric-hybrid powertrain.
The main work areas for crawler excavators in the 40-t (44-ton) class are high-volume earthmoving and laborious tasks in quarries and opencast mines. Such work cycles necessary for those areas offer a promising technical starting point for a driveline using a combination of different sources of power.
As would be expected, a diesel engine is the main source of energy for the R 9XX concept. It operates together with hydraulic and electrical energy storage devices—components newly developed by the Liebherr Power Train Competence Center and comprising the electric slewing gear, super capacitors, and the electronic control unit.
A pressure reservoir and generator are used to recover hydraulic energy. This combination of electrical and hydraulic powertrain features reduces fuel consumption while increasing load-handling performance.
The lifting cylinders are controlled without throttle valves to avoid loss of energy before the recuperation stage of the process is reached. When the working equipment is lowered, the energy released by this movement is stored temporarily via a hydro-mechanical energy generator in a hydraulic storage unit and the super capacitors. In this way, drive and storage take place without any losses due to the system.
The slewing gear is electrically driven and energy is also stored electrically. When braking, kinetic energy is converted into electrical energy in the generator and stored by the super capacitors. This energy is released again when the superstructure has to be accelerated as part of the machine’s operating cycle.
Power from the diesel engine can be supplied directly to the operator or input to the electrical energy store. In turn, the energy storage device can supply the slewing gear or the hydraulic pump drive to power hydraulic movements. The system allows energy to be transferred between the various part-systems, ensuring that the diesel engine only supplies the specific amount of energy that is needed. In addition, the load imposed on the diesel engine is much more uniform, with the resulting benefits of reduced component wear and lower fuel consumption.
The R 9XX concept’s hybrid system can make short-term peak power available up to twice the nominal output of the diesel engine. According to Liebherr, no crawler excavator using this principle has so far reached the market.