Minimizing operating costs continues to be a high priority for designers of mobile equipment, and hybrid drives represent a viable solution. No matter which sector a machine used, both electrical and hydraulic series solutions have established themselves on the market in an evolutionary process. In such cases, it is often a downsizing of the diesel engine that results in significant fuel savings with the aid of a hybridization. Depending on the machine and the work process involved, energy recovery functionalities can also make a contribution to energy efficiency.
Operation of an Asphalt Roller
Asphalt compactors with tandem rollers are machines that can benefit from hybridization because a typical operating cycle requires significant performance peaks and valleys for the diesel engine during reversing procedures. Depending on the machine version, dynamic compaction systems produce vibration of the roller drums rotating centrifugal weights powered by hydraulic motors. The necessary compaction power is applied by driving over the hot asphalt that was laid down shortly beforehand with activated vibration.
Figure 2 shows the simplified drive topology of a tandem roller. The traction drive is powered and controlled by a closed hydrostatic circuit with variable-displacement pump and fixed-displacement motors in the drums. The hydrostatic circuit provides both propulsion for the front and the rear roller drums.
2. This simplified schematic shows the layout of a standard drive system for tandem-roller asphalt compactor.
Potential for Downsizing
During a reversing procedure, the machine simultaneously decelerates and stops the vibration. These actions must be closely synchronized to achieve an optimum compaction in the asphalt. When starting up the machine in the opposite direction, the roller must be accelerated by the traction drive and the vibration drive must resume either in parallel or with a slight time offset. This results in considerable load peaks for the diesel engine,