Electrification & Hybrid Trends in Heavy Construction Equipment

By Rafael Cardoso, Engineering Manager, Mobile Systems and Software, Bosch Rexroth

In recent years, the construction industry has experienced a heightened desire for more sustainable solutions. Due to this, the industry is increasingly moving toward electrification of its equipment. The benefits of doing so, including greater efficiency, improved performance, quieter operation, and potential for automation, become more widely recognized. Electrification is a process that begins with the replacement of combustion engines with electric power sources, such as an electric motor powered by a battery.

Advances in battery technology have made it more feasible for the construction industry to move toward energy-efficient machines that require less maintenance. Electrification’s ability to dramatically lower carbon emissions is especially important for an industry that comprises 42% of combined global emissions. This carbon-neutral, cost-saving technology has both advantages and disadvantages. Depending on the application of each piece of equipment, different systems can be deployed, and each offers a range of benefits.

How Electrification Can Be Adopted in Construction

In construction equipment, electrification is typically relevant to drive and implement systems. Electrical components can be used for the drive system, focusing on acceleration, steering, and other functions. Electric systems are better suited for managing rotary motion, making them an excellent choice for drive systems.

Electric components can also play a role in Implement Systems, as seen in excavators where the boom, bucket, auxiliary functions, or blade are actuated using electric motors or linear actuators. Electrification in the implement system is seen as less effective and has not been widely adopted due to the historical effectiveness of hydraulics. This is particularly true for linear actuation, common in these systems especially within heavy pieces of equipment that require more energy and power density.

Smaller machines around 55 kilowatts (74 hp) or lower, e.g. compact truck loaders and mini excavators, are more suitable candidates for full electrification due to the lower power density required for operations. Heavier machines with over 100 kilowatts (134 hp) of power pose an additional challenge for a fully electric system. Although electrical components have evolved over the years, the high power density required for operating heavy machines, such as those in the mining industry, may still impose constraints for a fully electrified solution adoption.

Benefits of Hybrid Construction Equipment

Although a variety of approaches have been attempted, manufacturers are still working to achieve energy efficiency for high-power-density machines. Today, none have proven to be the clear leader in solving the complex issues to allow for industry-wide consideration. In the meantime, hybrid applications are helping to ease the industry toward more energy-efficient solutions.

One potential approach to off-highway vehicles involves adding an electric motor to drive a hydraulic pump that controls the implement circuit. In the construction industry, hybrid solutions have been successfully applied to diverse types of off-highway machines. This is true especially when lifting loads, rollers, graders, compactors, and sweepers.

Since combustion engines are only 30-40% efficient, the majority of energy created is lost through heat and noise. Conversely, electrical machines are moving the needle by reaching over 90% efficiency from battery conversion. This massively reduces the energy wasted through the process. Having said that, these efficiency advantages are not without challenges elsewhere, particularly as it pertains to machine downtime.

Compared to a combustion engine in an off-highway machine, charging the battery pack becomes an evident critical operation. Depending on the application, a battery pack can take hours to recharge. In comparison, a combustion engine takes only a few minutes to refuel. To maximize efficiency, strategic pre-planning of the machine’s daily movements is crucial for electrified machines, ensuring optimized energy use and downtime.

Amplifying Innovation in Electrification

Software-centered, electronically controlled machines are becoming increasingly common in the construction industry. Software-focused solutions enable more innovative approaches that can be applied to off-highway machinery, such as compact track loaders, aerial work platforms, or excavators. Improving efficiency in the hydraulic portion of a hybrid machine will be critical in these digital systems. Hybrid machine efficiency can be further enhanced by optimizing electro-hydraulic systems. Multiple approaches may be used, such as allowing energy recovery during movements assisted by gravity. An example of this is when a boom actuator moves downward.

In current systems, a single pump controls multiple actuators. However, due to varying pressure requirements among actuators, energy is inevitably wasted through throttling losses, as some actuators do not require higher pressure. Several approaches have been explored to address this issue, including displacement control and multi-pressure rail systems.

Displacement control directly regulates flow from the pump while fully opening the valve spool, minimizing throttling losses. This approach can be applied even in conventional systems when only one actuator is active at a given time. Additionally, incorporating multiple pumps could enable alternative displacement control architectures. In combination with software-centered systems, a multi-pressure rail system can reduce losses when combining the best pressure level with different actuators functioning at different pressure levels.  Among various options and architectures, approaches like these are particularly relevant for battery-powered machines using hydraulic systems. They help reduce downtime and optimize battery efficiency.

Additional Industry Applications

Now, let’s explore how electrification and hybrid trends can be utilized in this month’s focal areas for the Journal: the medical, food processing, and plastics industries. Both are increasingly applicable in all three industries, offering cleaner, quieter, and more energy-efficient solutions for operating machinery such as sterilizers, conveyor systems, and injection molding equipment while reducing emissions and enhancing operational precision.

In the medical industry, electrified equipment including imaging devices, surgical robots, and diagnostic machinery benefit from reduced noise, improved precision, and lower maintenance requirements. This is key to enhancing patient care and operational efficiency. Electrification in the food processing industry enables cleaner and more hygienic operations with reduced emissions, making it ideal for powering mixers, conveyor belts, and packaging systems in compliance with strict sanitation standards. Finally, hybrid and electric solutions in the plastics industry improve the energy efficiency of injection molding machines, extrusion systems, and recycling equipment, leading to lower operating costs and reduced environmental impact.

Connected Machines and Future Considerations

Telematics is the digital connection of heavy machines through advanced Internet of Things (IoT) capabilities. It can provide critical data to off-highway fleets, especially within electric machines. Whether a machine is preparing terrain, landscaping, or load moving, IoT and telematics systems can help determine the optimal configuration for maximum efficiency within a software-centered machine control system. The data from these actions can then be sent from the connected IoT and run through algorithms to improve efficiency.

Hybrids are becoming a viable solution for the future, whereas electrification still has room to grow before broader application. Electrification is a promising concept, but hydraulic components are not going away anytime soon. These systems will continue to play an important role in off-highway machinery, especially for linear movements and machines with high power-density requirements. Determining the optimal system for each construction application will need to be done on a case-by-case basis. This is especially important as innovations grow in digital, software-centered machines to provide a variety of benefits for an energy-efficient operation.