eXact – Electrification of the Next-Generation Construction Machine

In the eXact project, students from ETH Zurich, OST – Eastern Switzerland University of Applied Sciences, and FHNW University of Applied Sciences and Arts Northwestern Switzerland, in collaboration with SUNCAR AG, Volvo Construction Equipment, Ewellix, and other partners, developed a next-generation construction machine over the past five years.

The objective was to make the existing Volvo ECR25 Electric compact excavator more efficient, productive, and sustainable through targeted system innovations. In a first step, hydraulic components that cause significant energy losses were to be replaced with electric linear actuators. At the same time, automation, safety, and operator comfort were to be enhanced. In a subsequent step, the excavator’s last hydraulic main function was addressed: the swing drive. The goal was to convert this to a direct electric drive in order to completely replace the hydraulic pump and further increase energy efficiency.

• Drives: The three main cylinders (boom, stick, and bucket) were replaced with high-performance electric linear actuators. These drives, based on ball screw mechanisms, enable precise, low-loss power transmission. Challenges included integrating motors, gearboxes, and cooling systems within limited installation space, as well as protection against dust and impacts on construction sites.
• Controls: The control system was completely redesigned. All actuators, sensors, and safety functions are networked via a central control unit. Communication is handled through CAN bus networks, and emergency shutdowns ensure maximum operational safety.
• Artificial Intelligence: An augmented reality system provides the machine operator with real-time data visualization, including position, inclination, and working range. A custom-developed application also enables wireless data transmission and condition monitoring.

For the direct electric swing drive, the hydraulic base system of the Volvo ECR25 was first measured and analyzed to determine the required torque, moments of inertia, and energy consumption. Based on this analysis, a compact electric motor with integrated planetary gearbox and brake was selected. Electrical integration was accomplished via an inverter and the existing control system.

In the original Volvo ECR25 Electric, a central electric motor generated hydraulic pressure for all actuators—an approach that leads to significant losses, particularly through pump idling and throttling losses. By switching to electric direct drives, energy consumption was significantly reduced. The project created the possibility of recovering kinetic and potential energy during braking and feeding it back into the battery. This regenerative braking function leads to a significant increase in overall efficiency, as previously unused kinetic energy is made usable again. Through the combination of the higher efficiency of electric drives with the additional recuperation capability, the energy consumption of the swing drive was reduced by nearly 90%. Furthermore, digital control and regulation enabled an increase in maximum swing speed of approximately 30%. The efficiency improvement of the excavator arm with electric linear actuators ranged between 30% and 80%, depending on the application scenario. Efficiency is highly dependent on the specific work task: when digging in firm ground, the efficiency gain is lower, while it is significantly higher for work with lower loads—for example, during grading. The reason for this lies in the demand-oriented energy deployment of the linear actuator system: unlike hydraulic systems, where the pump operates continuously, the electric system only draws the energy actually required. The combined system of electric linear and swing drives confirms the potential of fully electric construction machines:

• Significantly increased efficiency through elimination of hydraulic losses
• More precise movements and reproducible control
• Improved workplace safety through integrated emergency stop and sensor monitoring
• Innovative user guidance through augmented reality-based display

Comparative measurements conducted during efficiency tests between hydraulic and electric systems revealed:

• 86.8% lower energy consumption per 10-minute swing cycle (254 Wh → 33 Wh)
• 89% less energy per cycle
• 25% more work cycles in the same time
• Significantly better controllability and reduced noise generation

The eXact project demonstrates that complete electrification of an excavator’s work functions is technically feasible and energetically beneficial. The project also showed that a fully electric swing drive for compact construction machines is technically feasible and enables enormous efficiency gains. The result is a nearly completely hydraulic-free, fully electric excavator with significantly improved energy consumption, controllability, and sustainability. Future work will focus on durability, robustness, and further development of the control system toward semi-autonomous applications.

ETH Zurich – Department of Mechanical and Process Engineering (MAVT)
OST – Eastern Switzerland University of Applied Sciences, FHNW University of Applied Sciences and Arts Northwestern Switzerland – School of Engineering
SUNCAR AG – Technical support and integration
Volvo Construction Equipment – Machine base and test support
Ewellix – Linear actuator