Learn the advantages and disadvantages of the four phases of electrifying mobile machinery — swapping diesel for batteries, optimizing hydraulics, recuperating energy, and going completely electric and eliminating hydraulics.

Mobile machinery power transmission is rapidly evolving, driven by regulatory pressures, growing demands for greener technologies, and reduced operational costs. In this article, we delve into the current trends, the viability of hydraulics, and the various levels of electric machines that are shaping the future of the industry. At the recent Danfoss Distributor Meeting, Chad Larish, Principal Engineer – Controls Division at Danfoss Power Solutions, presented gave a high-level overview of where off-highway technologies are now and where they’re going in terms of electrification.

Current market trends

The push towards electrified mobile machinery is gaining momentum worldwide, spurred by stringent emissions regulations and a desire for sustainable practices. Zero-emission zones in Europe and select U.S. cities are compelling Original Equipment Manufacturers to develop electrified machines. Moreover, total cost of ownership considerations, including maintenance savings and reduced fuel costs, are driving interest in electric alternatives across various applications from construction sites to warehouse operations.

 

Applications with confined operations or within city limits are key markets moving away from diesel, Larish noted. One machine use that’s transitioned to a majority of electric is the aerial work platform, he said. “In China a few years back, only about 30% of aerial work platforms were electrified, and we’re seeing now upwards of 70% are electrified machines,” Larish said. “That’s not driven from a regulatory standpoint, it’s really driven around where these machines are used and how they’re used. A lot of them are used on construction sites where power is available, and so they don’t have to pay for fuel. They have a two-day runtime, and they don’t have to pay for all the maintenance costs. So that’s kind of a big driver for that platform.”

Compact machines or those with shorter runtimes are a clear choice for electrified equipment, Larish said. Engine downsizing or elimination has always been the goal, but it’s easier with compact equipment with low-duty operation that have perhaps a four-hour run time and can be easily charged on a city’s power pole, for example. There’s greater interest in mid-sized utility machines and confined equipment that is running in a yard or an airport where it’s a fairly small environment.

Because charging infrastructure is a challenge and actual runtime is only about 3 hours compared to published 4 to 6 hours, OEMs need to find ways to get electric machines running up to a full day. Simply adding more batteries is not plausible due to added weight and costs so this is where hydraulic inefficiencies must be addressed.

If you simply make the prime mover swap of diesel to battery power, a compact machine becomes about 85 to 95% more efficient, Larish noted. But then you must take into account losses such as compressibility losses in the pump, through the valves, and finally, multifunction losses. This is why manufacturers are looking at various ways to electrify their machines.

Phases of electrification

1. Phase one: electric prime mover

The easiest move into the electric space is simply to swap out diesel engines for batteries without making any other fundamental changes to the system. Batteries are integrated to power electric motors, marking a fundamental shift towards electrification. These early-generation machines are primarily focused on functionality and learning the dynamics of battery integration. “A lot of this comes down to customers who are trying to learn about electrification. They don’t want to change too much. They’re trying to figure out batteries and the voltage standards. And of course, the challenge is that they don’t run very long,” Larish said.

2. Phase two: optimizing hydraulics

With battery-powered machines, hydraulic inefficiency is much more noticeable. Thus, it becomes necessary to optimize hydraulic systems to enhance machine efficiency and runtime. Advances in hydraulic technologies aim to minimize energy losses through improved pump designs and intelligent flow management systems. This phase represents a holistic approach towards maximizing the benefits of electric power while retaining hydraulic efficiency where necessary.

There is no one size fits all when it comes to increasing hydraulic efficiency, Larish said. Perhaps you can retain your existing pump — a fixed-speed, variable displacement pump, or perhaps you use variable speed, variable displacement, or variable speed, fixed displacement. But no matter what you choose, you need to provide flow at its highest efficiency, which requires more coordinated control between your electric motor, pump, valve, and demand, which will require more intelligent machine intelligence than with a traditional machine.

For fixed displacement pumps you cannot change displacement, so flow is dependent on speed. They are most efficient at higher flows and lower pressures or lower torques and as you increase torque and reduce speed, efficiency tends to drop off. Additionally, on dynamic machines with varying flows, the constantly changing speed can generate noise that an operator may find undesirable.

Variable displacement offers you a little bit more flexibility. You can reduce swashplate angle, and reduce displacement and increase speed run the motor optimally.

Next, using variable margin control allows for better optimized hydraulics, in which you can figure out how much margin you actually need in your circuit, then reduce that margin to exactly what you need. Danfoss tested this in a forestry application in Finland, where they were saving about 10% fuel economy doing variable margin control through electronic load sensing.

The company’s Digital Displacement Pump technology is at the forefront of maximizing hydraulic efficiency, especially when combined with its Editron tech. Digital Displacement pumps use solenoid valves to control each cylinder on a shaft-turn-by-shaft-turn basis. The technology offers a fast response rate and reduces energy losses by up to 90% compared with conventional pumps.

3. Phase three: recoverable energy

This phase explores the potential of recuperating energy during machine operation. Technologies like regenerative braking, where energy from lowering booms or braking motions is captured and stored, are being integrated into certain applications to further enhance efficiency and reduce overall energy consumption.

Recuperating energy back to the battery is the wish for many platforms, however the potential energy savings must justify the additional system complexity and cost. Additionally, any recuperation architecture changes must not sacrifice existing performance, functionality, and safety.

Regeneration reallocates hydraulic oil from a pressurized cylinder to somewhere else in the circuit to backfill the cylinder. This allows the function to lower by gravity and mitigates the need to use pump flow.

Applications that are looking at recuperation versus regeneration are usually those that have single function operation, such as a lifting function.

4. Phase four: electromechanical actuators

Machines that eliminate traditional hydraulic systems altogether opt for electromechanical actuators. While promising for specific applications, such as urban environments or controlled industrial settings where access to battery charging is easy, these systems face challenges related to cost, complexity, and operational robustness compared to traditional hydraulics.

“There are several prototype-ish platforms out there that are using EMAS, but they have their own challenges. They’re not quite as efficient at recuperating energy. They’re also not as shock tolerant as hydraulics,” Larish said. “So, there is some level of additional design requirements that go into fully electric.”

In this realm are electrohydraulic actuators or EHAs, which feature a hydrostatic arrangement. These pre-packaged units are typically seen on the industrial side of hydraulics. Then come core electromechanical designs such as ballscrew, roller screw, rack and pinion, and even flat belt technologies. These technologies have between 60 and 85% efficiency versus hydraulics, which are in that 40% range. The challenge with many of these actuators is that they often are big and bulky. They also require additional protection because they are generally not as shock and vibration tolerant as hydraulics. Rack-and-pinion and belt drives are more capable of recuperation, but ballscrew and roller screw are not quite as efficient at recuperation. Finally, these actuators can be more cost-prohibitive, which in turn makes the end machine much more expensive.

Challenges and considerations

• Efficiency concerns: While electric motors are highly efficient (85-95%), challenges persist in optimizing overall system efficiency, particularly in hydraulic subsystems where losses can occur through pumps, control valves, and flow regulation.
• Cost and space constraints: The cost of battery technology remains a significant barrier, with many customers reluctant to accept machines that exceed double the cost of diesel counterparts. Additionally, integrating additional batteries poses spatial challenges, particularly in compact equipment where every pound counts.
• Application-specific solutions: The journey towards full electrification varies by application. While compact equipment and aerial work platforms have seen substantial electrification due to operational benefits and regulatory compliance, heavier machinery like 25-ton excavators or machines used in remote areas face hurdles related to charging infrastructure and high-power demands.

Future directions and innovations

Looking ahead, the industry is poised to explore hybrid solutions combining electric and traditional power sources to balance efficiency, performance, and operational costs effectively. Innovations in battery swap technology and advancements in hybrid architectures promise to address the diverse needs of different applications while continuing to push the boundaries of mobile electrification.

While mobile electrification represents the future of cleaner, more efficient machinery, the move towards more mobile electric fleets is complex. From optimizing existing hydraulic systems to exploring advanced electromechanical solutions, OEMs and customers alike are navigating a complex landscape of technological innovation and regulatory compliance.