56 November/December 2023 | E-Mobility Engineering The boom that holds the bucket arm is powered by a closely integrated EH linear actuator mounted in the hydraulics compartment. The actuator replaced the original boom hydraulics, and Baettig describes it as an integral part of the effort to increase the machine’s overall efficiency. “Decoupling the boom from the rest of the hydraulics reduces losses in the hydraulic system substantially, as the boom often represents the actuator generating the highest hydraulic pressure in the system,” he explains. “Having a separate hydraulic actuator for the boom further allows for the elimination of valves that typically contribute to hydraulic losses.” HELAX technology The actuator system selected is the decentralised Hydraulic Electric Linear Axis (HELAX) from Bucher Hydraulics. It is decentralised because instead of relying on a central hydraulic pump that feeds fluid to multiple cylinders via a system of valves, it provides each cylinder with its own electrically driven pump, an arrangement that gets rid of the need for any valves, the above mentioned inefficiencies of which result from throttling losses. The hydraulic system is selfcontained, with its own reservoir/ accumulator and hoses, so it needs only an electrical connection and physical mountings to operate, and the hoses allow the pump to be conveniently positioned remotely from the cylinder. The design of the 14-cylinder highpressure AX pump ensures smooth running with minimal pulsation. CAN bus-controlled, the drive system consists of an inverter, speed-controlled servomotor and AX pump and cylinder, and operates at up to 82% efficiency, according to Bucher Hydraulics. Like the slew drive system, the EH boom system allows for recuperation/ regeneration of energy, but both hydraulic and electrical in this case. Which of them contributes the larger share of the recuperation depends on the boom’s duty cycle, Baettig notes. The recuperation capability in the EH linear drive is provided by the AX hydraulic pump, which can electrically return energy from the hydraulics via the pump and the electric motor. This is different from a conventional hydraulic system in which pressure built up in the system as it performs work is relieved by returning the fluid to the tank that serves as a reservoir, dissipating the energy. “In general, our goal is to maximise the recuperation potential while the driver should not actually feel the difference between a conventional machine and the electrified version,” he adds. With the traction drives, the situation is similar to that affecting electric cars, in that the amount of recuperable energy depends largely on the operator’s driving style and the ambient conditions. “While driving on level roads the electric motor should allow for a high level of recuperation,” Baettig says. “However, abrupt or emergency braking will not be supported solely by the motor but also by conventional braking mechanisms.” Along with reductions in energy losses, recuperation is expected to make a major contribution to efficiency, according to Suncar’s simulations. The company estimates an energy saving of around 18% through the use of electric drives, with an estimated further 30% equivalent saving during driving enabled by recuperation under braking. In percentage terms, the gains look even greater for the EH system over conventional hydraulics, with energy savings of 75% thanks to new hydraulic pumps and recuperation in both the slewing drive and digging/boom operation. Another electrically driven hydraulic device, the brake and pilot pump, serves as an auxiliary to power the lowpressure hydraulic circuit. This 24 V device guarantees hydraulic pilot and brake pressure in the event of a failure in the HV battery, drawing power from an LV battery via its own inverter. Baettig explains that as this pump runs almost continuously, the focus was on silent and quiet operation. Component distribution In terms of physical distribution, this componentry is divided between the upper carriage and the undercarriage. The following applies to the second of the two prototypes, which is electrified to a higher degree and is more representative of eventual production machines. CAD view of the ZE150W’s undercarriage, showing the position of the HV rotary joint, electronics modules and hydraulic cylinders that operate the backfill blade
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