Electrification is a global trend that offers the potential to fight climate change. For mobile-equipment builders, that means intelligently melding hydraulics and electric drives. At the recent Fluid Power Technology Conference in Cleveland, Danfoss Senior Systems Engineer Simon Nielsen discussed the changing off-highway landscape and how his company is positioned to take advantage and benefit its customers. Here are some of his key take-aways.
At recent mobile-equipment shows like bauma and Agritechnica, and likely soon at Conexpo, discussions about electrification are a part of almost every vendor’s booth. And we’re seeing the beginnings of conceptual work and the first market offerings of electrified machines. At Danfoss, we believe electrification is here to stay. It will create new opportunities in our markets and, honestly, take away some market share from hydraulics over time. With all of this in mind, how have we responded? We like to say it’s part of our Danfoss DNA that as the times change we invest and innovate to remain successful. And that’s what we have especially been doing the last few years with several acquisitions and partnerships.
We recently announced a strategic partnership with Autonomous Solutions Inc. We’ve acquired Visedo and Axco Motors out of Finland and UQM, a well-known electric drives company in Colorado. And my point here is that we don’t see this as an either/or situation. Some companies could choose to ignore the changes and double down on hydraulics, and probably be profitable for many years. We have taken more of the role of becoming a multi-technology specialist. And we think it’s an inevitable symbiotic meshing of technology that is taking place over time — each technology will play a role in the control and transformation of power, and we intend to leverage both.
The new acquisitions are part of our Editron business segment, and they bring know-how in electric drives, energy storage devices, as well as software. And just as important, we gained years of experience for electrification in on-highway, off-highway and marine markets. These systems offer power levels from 40 kW all the way up to 4 MW, and efficiencies as high as 97% over a broad operating range. That matches off-highway machines that typically operate across a range of conditions, speeds and torques. Additionally, the products are ruggedized with a high seal rating and a great tolerance to shock and vibration.
What does it mean for the future of powertrains? The conventional system architecture used for decades has an engine as the prime mover; propulsion provided by a closed-circuit hydrostatic pump and motor; and usually work functions through an open-circuit system and a valve group.
But bringing electric machines into the mix gives new options in various ways. Perhaps the smallest journey away from the conventional architecture is the parallel hybrid, where we connect an electric system with energy storage to the engine. This gives the option to both add and subtract power from the drive train in situations like regenerative braking or peak shaving of momentary high loads. That could even lead to downsizing if the engine can be sized for average loads. And if there is a clutch between the engine and drive train, we can temporarily operate in a purely electric mode, depending on energy storage capacity — useful for momentary zero emission operation, like passing through a tunnel.
Another version of hybridization is the series hybrid. The key distinction here is that we replace the hydrostatic drive train with two electrics, one on the engine operating primarily as the generator and the traction drive operating primarily as a motor. It also has energy storage so again, there’s the possibility for recovering energy, operating in pure electric mode, productivity improvements and peak shaving.
We’ve seen series hybrid applications that have reduced fuel consumption by up to 50%, which is really remarkable. The significant point is that we are replacing the drive train. If we previously achieved customer requirements for torque and speed with a hydrostatic or mechanical drive train, we are now meeting them with the electric drive train.
And when we want to get into zero emissions, and really the best efficiency improvements, we start talking about full electric. This is where we are typically using at least one electric motor sourcing energy from a battery. For example, Paus in Germany produces a lot of custom and niche construction, mining and utility machines. They have replaced mine vehicles that have a traditional diesel and a hydrostatic drive train with a full electric system running off of a battery, and lowered their energy cost by 50%.
Ventilation in mines is expensive, and anything that eliminates exhaust has a direct benefit on the bottom line. Additionally, the electric drive train has lower noise, vibration and heat, all things that are valued in a mine. Battery size in this vehicle is around 50 kWh, on the order of what we find in electric cars on the market today, which gives them three to four hours of operation.
Another version of the full electric vehicle is where we don’t want to eliminate the existing drive train. Maybe it’s very hydraulic in nature and we decide to instead to swap the engine with an electric motor. This is a fast and valid way (maybe not the most optimal way in all cases) to achieve a battery electric vehicle. And this is exactly what we have done with Pon Equipment, a Caterpillar distributor in Norway that converted a number of a CAT 323F excavators by replacing the engine and adding a 300 kWh battery pack in place of the counterweight. This gives them five to seven hours of quiet, emission free, efficient operation. In Norway, there are targets for zero emission construction sites, particularly in cities, as well as a goal for carbon neutrality by 2030. This kind of technology will enable them to meet those very aggressive goals.
I’ve given a lot of treatment so far to rotary actuation, but what about linear functions? This is where we look at off-highway machinery at the core. A big part of hydraulics is cylinders and linear movement for work functions. And definitely, this is where hydraulic cylinders have been the standard for a long time. They are still difficult to beat in terms of robustness, low production costs, high force density and overall simplicity. They love operating in dirty conditions and mud and water, and they are relatively efficient.
But they also get a lot of criticism. We see open-circuit systems criticized for throttling and idling losses. There’s been research in recent years looking into improvements in valve technology, as well as in displacement-controlled actuation — getting rid of the valve for metering and throttling components and dedicating pumps to the flow. Electric vehicles have a different power source, so now people are saying let’s shift that control and transformation of power over to an electric source. And they’re distributing it more and more throughout the vehicle. So far it’s only in the concept and research stage as far as we can see, but there is interest.
And many companies are coming forward with electric pump drives, electrifying the production of flow while keeping the same actuator. This is an area where Danfoss is also working with our Digital Displacement technology. This involves an acquisition and partnership with Artemis Intelligent Power. We are commercializing this Digital Displacement Pump (DDP) technology and, in the future, additional products including motors. This radial-piston design has digital control for fast and accurate control of displacement and flow from the pump, along with very high efficiency, even at low displacements and partial loads.
Compared to conventional bent-axis and swash-plate technology, we believe it’s a game-changer in terms of hydraulic technology. And it is available with either a single outlet, like a conventional pump, or with multiple outlet ports as well.
We have been exploring this technology at our Application Development Center in Ames, Iowa. We purchased a new, next-generation Cat 320-series excavator with electrohydraulic controls, a machine Caterpillar touted as offering major improvements in efficiency and productivity over their previous models. We conducted a series of baseline tests and mass excavation and trenching operations to establish how the machine performs. We then essentially swapped pumps, removing the original axial-piston swash plate pumps in tandem and replacing them with a DDP pump stack in tandem, keeping the engine machine controls the same.
Then we repeated the tests with impressive results. In max excavation, the DDP machine was 16% more productive by weight (tons per hour) and 7% more productive by efficiency (tons per liter of fuel burned). In trenching tests, we could dig and fill 15% more per hour while consuming 13% less fuel.
Keep in mind this is against an already very impressive machine. It isn’t pilot controlled and is among the best on the market. And definitely, the results can be attributed not only to the static efficiency improvement of DDP, but also improved responsiveness and controllability of the pumps.
So this may beg the question, is there a place to combine the most modern hydraulic technology with some of the best in electric powertrain technology as well? We know that in the world of battery electric vehicles, the main concerns are range, size of the battery and cost. We believe that DDP could be a tool in reducing the power need of the vehicle as well as battery capacity and costs.
Our own analysis has shown that if we took that battery electric Pon excavator and converted to a Digital-Displacement system with multiple outlets on the pump as well as an improved control valve architecture, that we could match the working capability of the machine with 20% to 25% less battery capacity. The machine has a 300 kWh battery pack. Keeping in mind that the going rate for battery capacity is about 500 euros per kWh, if you reduce that cost by 20% to 25%, that easily pays for any hydraulic technology improvements.
I’ve given a lot of treatment to the benefits and advantages of electrification. It wouldn’t be fair if I didn’t talk about some of the challenges. First and foremost, energy storage and charging infrastructure. We are definitely looking at different energy densities and refueling/recharging rates compared to fossil fuels. Battery energy densities and charge capabilities continue to get better, but it is still a challenge.
And again, electric machines are short in power torque and force density compared to hydraulics, which can be limiting factors in various applications. With the current price of hydraulic components, it can be difficult to justify that higher initial cost of electric drive trains, even if the total cost of ownership over time proves to be favorable. And on the personnel side, lot of our workforce is mechanically inclined and experienced in conventional technology. A shift to electric drives will pose challenges to good field service and customer support.
Customers must consider many trade-offs in choosing the best type of system. Danfoss has developed digital tools such as its Design Center that helps put our expertise and knowledge in the hands of customers. Future capabilities of this tool should include the ability to perform comparisons on various electric and hydraulic drive trains. Overall, our outlook is that the market will become more diverse, with electric and hydraulic technology becoming more integrated.
Mobile hydraulics, definitely in the short run, has some unique advantages that are going to be difficult to replace. And we still very much believe that any improvements in drivetrain efficiency, especially hydraulic system efficiency, will continue to have merit, not only for battery electric vehicles where it translates directly into range and battery size, but on any system that is seeking to minimize fuel consumption and reduce emissions.
And as a final word, there are many companies joining the electric revolution, ranging from traditional engine manufacturers to producers of gearboxes and axles. I think that the hydraulic suppliers have some advantages here. For decades we have been working with continuously variable transmissions, vehicle power management, controlling engines and gearboxes, and offering customized application software literally hand-in-hand with the customer. As you’re choosing a partner for moving forward with electrification, keep all these things in mind, especially as electric and hydraulic technology come together.
Danfoss Power Solutions