Hydraulic systems have long been necessary for off-highway mobile equipment because of their power density, among many other key attributes. However, driven by a variety of factors – including regulatory trends and advances in technology and customer economics that make it possible – electrification is now being seen as the way of the future.
Industries as diverse as construction, mining, refuse, agriculture, oil and gas, marine, forestry and many more are working feverishly to rethink their operations and their equipment in an effort to adapt to one of the biggest game changers to impact consumer and commercial markets in decades.
According to a 2019 study by 360 Research Reports, the worldwide market for electric vehicles for construction, agriculture and mining was expected to grow at a CAGR (compound annual growth rate) of 51,3% between 2019 and 2024. By 2024, the market is predicted to be worth $2,27 billion. A September 2020 report by Markets and Markets predicted a 22,8% growth in sales of electric off-highway vehicles between 2020 and 2025.
Electrification is by no means a new topic, however. As part of the larger conversation around clean technologies, electrification has been discussed for many years. What makes the conversation more meaningful today, however, is the convergence of three powerful forces: stricter governmental regulations; ESG (environmental, social and governance) initiatives by the top companies in the world; and TCO (total cost of ownership).
As adoption rates for electric passenger cars accelerate, industry experts predict an increased migration of electric technologies into larger, heavier equipment which has, to date, been somewhat limited (depending on the industry) as a result of insufficient and inefficient power sources.
Paul Horvat, vice president of business development for Parker Hannifin, describes the government’s role in driving electrification as a carrot-and-stick approach that combines lucrative incentives with severe penalties, to motivate companies to utilise cleaner technologies and decrease their reliance on more traditional energy sources that create higher levels of emissions.
Breakthrough technologies are making possible the electrification of more machines than ever before imagined. While some in the industry may look at the electrification glass as half empty, pointing to remaining challenges and limitations of current battery capabilities and other green energy sources, according to Mark Czaja, chief technology officer for Parker, it is important to remember that it also took a long time to get combustion engines to where they are today. Patience will be key in allowing existing electric systems to evolve.
This article explores how hydraulic components, electrical machines and vehicle controls are coming together to optimise machine performance, and how they are positioned to meet future challenges.
No complete replacement for hydraulics
The amount of money being invested in new research and electric technologies is unprecedented. Global automakers are planning to spend more than half a trillion dollars on electric vehicles and batteries through 2030, according to a Reuters analysis, amping up investments aimed at weaning car buyers away from fossil fuels and meeting increasingly tough decarbonisation targets. Less than three years ago, a similar analysis by Reuters found that car companies planned to spend $300 billion on EVs and related technologies.
All this investment is being made in the hopes that electric systems will one day be the norm. But that doesn’t mean they will be everywhere. Hydraulics for work functions, in particular, is not going away any time soon. There will likely always be some applications that are best served by hydraulics.
Hydraulics is unique in the world of power transmission because it owns the trump card of power density. There is no more compact method of mechanical actuation than with hydraulics when considering power-to-size ratio, according to www.mobilehydraulictips.com.
Hydraulics is not replaceable, but adding electrics can improve performance and decrease noise levels. Indeed, the most promising technologies are those that combine the best of hydraulics with the advantages of electric. Industries continue to work toward ways to integrate electrics into existing platforms in the most effective ways possible, making maximum use of the power density and efficiency provided by hydraulics technology.
Many OEMs are taking a phased approach to electrification, starting by replacing diesel engines with electric motors and batteries. They will put in as much battery power as needed to get a decent day’s work out of the machine but keep the rest of the circuit the same, according to www.oemoffhighway.com.
Others are leveraging opportunities to recover energy through the hydraulic system. The right technology can help store energy in a hydraulic accumulator or in the battery system through the electric motor that drives the hydraulic pump, enabling the electric motor to effectively run as a generator when travelling downhill or during deceleration, for example. This process is already common in hybrid consumer vehicles, where electric motors recover energy as the car brakes.
However, better hydraulic and electric component integration is necessary to achieve the greatest efficiencies. Hydraulic pumps and the electric motors that power them must work together in harmony; smarter hydraulic components that can sense load requirements and opportunities for energy recovery are needed to achieve efficiency gains. Additional effort is required to ensure all components and subsystems are contributing to an holistically smarter, more efficient vehicle or machine.
The marriage of hydraulic and electric designs
Horvat describes the intersection between the domains of hydraulics and electrification as the place where most of today’s innovations are taking place. “We have a whole new playground where these two technologies converge, but we need to rethink how to do these modern machines,” he says.
Chris Griffin, electrification business development manager at Parker, adds that the goal is to bring together the best of hydraulics, such as robustness, with the controllability and precision that comes from an electrical approach: “We need to leverage traditional technologies but rethink them, intelligently melding hydraulics and electric drives with the aim of using the benefits of electrification where it is technically feasible and where the value is most appreciated.”
Finding exactly that right balance, however, is not always easy. As mobile machine builders approach drivetrain electrification, a major concern is balancing the need to deliver enough torque to drive the machine against the need to make the most economical use of electric power.
Just as with the drivetrain, engineering the drive elements for the maximum load an implement needs to lift or move is one critical calculation. Consider a full-size excavator that must dig and move thousands of kilograms of soil or rocks all day long. Today, that implement is typically hydraulically driven, drawing its pressure and flow from a pump powered by the mobile machine’s diesel engine.
In an all-electric system, it is possible to power that implement with a heavy-duty electric motor powering a ball screw or other linear component to do the work. However, the size of the actuator to accomplish the task and the drain on the battery could be substantial, even for a hybrid electric platform.
A more effective solution would combine electric power and hydraulic power. It takes a certain amount of power to move a given load – whether it’s voltage and current with an electric motor, or flow and pressure with a hydraulic cylinder, the ultimate result is generating the torque needed to do the work. Rather than powering the hydraulics from the diesel motor, the motor runs a generator which, in turn, supplies power to an electric motor driving the open-loop hydraulic pump for the cylinders powering the excavator’s tools. This leverages the proven power density of hydraulics while transitioning how it is powered from the combustion engine platform to electric power.
An important lesson to emerge from all the efforts to optimise the combination of hydraulics and electrification is that an holistic approach must be taken. Looking at individual components accomplishes little without considering how they contribute to the overall system, including the motor, controller, e-pumps, sensors, VCUs and noise isolators, to name just a few critical components. An effective strategy focuses on maximising the overall hydraulic system efficiency. Key considerations for achieving this efficiency include weight, range and the integration of different components that will communicate with one another.
Challenges remain on the road to electrification
It is easy to understand the attraction of electrification. Electric power transmission is clean, efficient and accurate up to levels that hydraulics can’t match. However, despite all the advances and hype around the potential for electrification, barriers still exist.
While breakthrough technologies mean batteries can charge faster, last longer and be lighter in weight, some of these newer technologies will not be fully commercialised until the end of the decade. The reality is that a large percentage of batteries on the market today are still heavy, expensive and not able to meet demand.
Tesla is one of the companies best recognised for its focus on scale and cost. Horvat notes that, as a result of work done by companies like Tesla, historic battery costs of $140 per kWh will realistically be down to $50 per kWh in the near future.
“The cost and performance of batteries have improved significantly in recent years, but we’re not quite there yet,” Czaja says. “We are still playing catch-up. This is a journey and the transition to electric won’t happen overnight.” He also points out that while the viability of electric machines is more real in certain industries, there is still not enough power density available for all applications.
This explains why adoption rates of electrification are, for the most part, much higher in lighter-weight vehicles, and lag in industries where heavier machines dominate.
Despite impressive developments, neither batteries nor fuel-cell technologies are ready to meet the very high-power requirements needed for the harsh conditions to which many heavy-duty vehicles (especially in the off-highway segment) are exposed. Some trucks require several megawatts worth of power and are exposed to extreme vibrations and heat development, as well as dirt in the air. ICEs (internal combustion engines) have met these requirements for decades, but electric systems are still in development.
“We should be optimistic but not unrealistic about ongoing challenges with battery technologies,” said Nils Henriksson, business development manager at Parker. “Battery energy density is two orders of magnitude lower than diesel. While a 20 litre diesel tank stores 200 kWh of energy, a similarly sized battery pack stores 5 kWh. The energy density of a diesel tank is 10 kWh/litre vs. 0.16 kWh/litre for a battery pack.”
Another challenge, according to Henriksson, is energy transmission. It takes 45 seconds to fuel up that 20 litre diesel tank. This compares with the 33 minutes it takes to ‘fuel up’ a similarly sized battery pack at a robust 25 kW charging capacity.
Sufficient infrastructure is also lacking. There simply aren’t enough charging stations to support a large percentage of consumers converting to electric vehicles, for example. And there is industry-wide doubt that sufficient renewable energy sources currently exist.
Yet another concern impeding widespread application of lithium-ion batteries is thermal management. The reality is that thermal conditions inside an electric vehicle are markedly different than those with an internal combustion engine.
Thermal management in electric vehicles is especially critical since it has been shown that it can lower degradation rates for the lithium-ion cells in operation, therefore increasing battery pack lifetime.
This impacts not only lifecycle cost but also the environmental impact of the battery during its entire lifecycle. In other words, the environmental footprint incurred during battery production can be counterbalanced by extending the useful life of batteries. Moreover, this increases material resource efficiency and decreases the pressure on the supply chain for critical raw materials, such as lithium and cobalt. In this way, thermal management systems not only impact safety, but also cost-efficiency, high performance and sustainability of a battery pack, according to www.automotiveworld.com.
A problem remains, inasmuch as the current generation of thermal management systems is sub-optimal. Surface cooling dominates the electric vehicle market, yet published research suggests lithium-ion cell lifetime can be tripled if tab cooling is implemented effectively in the battery pack design. The shape and size of lithium-ion cells varies enormously across the market, bringing considerable variation in thermal performance, such as how the cell behaves when internal heat generation raises its temperature.
Significant research is being undertaken to identify new materials and heat-resistant power electronics to help minimise the heat, which is key to improving the overall safety of the vehicle and maximising battery charging speed, longevity and overall lifetime. Thermal runaway is a real fear for batteries.
This effect occurs when a single cell within a battery pack becomes too hot, causing neighbouring cells to ignite in a fire or, in more severe cases, an explosion (according to www.allaboutcircuits.com).
Thermally conductive potting compounds are a growing method for effectively conducting heat away from power components to the heatsink. Using thermal management materials that provide a unique combination of high thermal conductivity and low viscosity reduces both maximum temperature rise, and the time it takes to reach a stable temperature while maintaining electrically insulating properties. Such benefits improve efficiency and component lifetime, thereby enabling high-performance chargers and power electronics.
It is no longer an affordable proposition to think of thermal management as an unnecessary cost. Longer battery life, higher performance, safer use and better value require tailored thermal management solutions.
The key driver is to minimise the energy storage size, which will reduce installed cost at manufacturers and for the machine owners, as operating hours increase between charging. Electrification also provides the freedom to design new power trains and hydraulic system concepts due to the decoupled layout.
Hybrid is today’s reality
While battery technologies continue to evolve and overcome challenges that have previously restricted more rapid electrification adoption rates, hybrid electric systems are well positioned as an ideal interim solution. This is especially true for larger machines with longer duty cycles that are not ideally suited for fully electric systems from a TCO perspective.
Hybrid electric equipment combines the power density of a diesel engine with the emissions-cutting capabilities of a battery. It contains a smaller diesel engine alongside a rechargeable battery and electric motor, making it ideal for both high-intensity jobs and locations that require low emissions.
If designed correctly, the battery used in a hybrid system can be relatively small and function as a buffer that allows the pump and engine to produce work at higher speeds where the efficiency is best. The engine is not loaded at idle which reduces fuel consumption, emissions and noise. The pump size can be reduced by up to 40% because its speed is no longer tied to the engine’s idle condition. This produces several other advantages in terms of cost, weight and installation.
Hybrid drives still burn diesel fuel, but they can recover and reuse energy that would otherwise be wasted as heat. This can lead to downsizing if the engine can be sized for average loads. If there is a clutch between the engine and drivetrain, the vehicle can be temporarily operated in a purely electric mode, depending on energy storage capacity. The hybrid system also allows OEMs to design certain auxiliary functions as ‘power on demand’, using electric motors that are not drawing from the engine all of the time. An example is an electric fan being used in lieu of a belt-driven fan.
Another version of hybridisation is the series hybrid, in which the hydrostatic drivetrain is replaced 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 there is the possibility for recovering energy, operating in pure electric mode, productivity improvements and peak shaving.
Hybrid systems, which have largely been used to power work functions but have also effectively been used to power propel functions on large trucks and buses, offer significant benefits. In some applications, they have reduced fuel consumption by up to 50%, according to www.mobilehydraulictips.com.
It’s not just about batteries
Battery technologies currently represent the greatest potential because they lead the way in adoption rates as well as in technology advancements. This explains the market’s disproportionate focus on battery-electric powertrains. However, there are other sustainable options.
At present, there are four true zero-emissions technologies to power vehicles, of which battery electric vehicles (BEVs) are one. It is important to note, however, that BEVs are only carbon neutral if charged solely with renewable power. They can, in fact, lead to high carbon emissions when charged with grid electricity, as is the case in most regions today.
The other zero-emissions technologies include hydrogen fuel cell electric vehicles, hydrogen internal combustion engines, and biofuel or synfuel internal combustion engines. The use of internal combustion engines with fuels such as bio methane and green hydrogen offer the greatest potential in the short term.
Fuel cells are electrochemical devices that combine hydrogen fuel and oxygen from the air to generate electricity and water. This means that hydrogen goes in and water comes out, with no pollution.
Fuel cells work like batteries, but they do not run down or need recharging. They produce electricity and heat as long as fuel is supplied. Hydrogen fuel cells can refuel rapidly, carry heavy cargo due to the system’s efficiency in storing electrons, and remain quiet during operation as they have fewer moving parts.
In addition, fuel cell electric vehicles have a much higher energy density by weight, allowing them to overcome the range and weight challenges associated with battery electric vehicles. Hydrogen tanks are also more compact and lighter than an array of fully charged batteries.
An additional advantage of this approach is the ability to keep the actual internal combustion engine with 20% engine evolution (upper part of the engines including the valving). This minimises the amount of redesign work necessary. However, there are some additional considerations, such as temperature control, sensitivity to vibration and shocks, and the lack of infrastructure to get these newer fuels on site. In addition, these fuels cannot readily be integrated into all mobile machines on the market today. It takes a lot of electricity to produce clean hydrogen, which means a potential drain on the grid.
Whether battery or fuel cell technologies are chosen, it is important to consider the domino effect of changing technologies. The skills and training necessary to properly maintain and service these new systems cannot be overlooked. Hydraulics professionals, long schooled in the details of hydraulic operation, need to learn new skill sets and be educated on new issues and specs.
The future is electric
As mentioned previously, the concept of electrifying work systems is far from new. But a long history of innovations has certainly changed what electric machines can do and how they operate today.
Driven by successes in the automotive industry, interest in electric machines is at an all-time high. The last few years have seen an acceleration in the electrification of vehicles and equipment, even in heavier equipment (although this adoption rate has been slower). Given the current pace of technology development, many in the industry expect a greater and faster shift to electrification beyond 2030.
The reduction of battery costs, for example, has been a huge enabler, making battery technologies more affordable and attractive. Digitalisation trends have made a huge impact on system operations, performance monitoring and predictive maintenance. These trends, while applying to hydraulic, pneumatic and electric systems, have the greatest relevance on electric systems which typically have more microprocessors to provide more information.
Greater connectivity, which allows individual components to communicate, allows for in-depth analysis of how well the entire system is operating and can ward off problems. For example, there are e-pumps driven by sensors that limit the pump’s speed if the fluid is too cold to optimise the performance while securing the function, because of the high viscosity.
As part of the effort to fast-track electrification-enabling technologies, there is an unprecedented level of collaboration taking shape. OEMs, suppliers and industry leaders have come together to share their knowledge in the hopes of identifying smarter solutions. Recognising the value of technology transfer and the exchange of ideas, Parker created its Motion Technology Center (MTC) which is a joint endeavour between Parker Aerospace and Parker’s Motion Systems Group. The MTC was created to provide a larger view of the various products and expertise that exist across technologies, in an effort to facilitate electrification solutions. It is expected to prove especially valuable when addressing emerging technologies that will be relevant in the next 10-20 years.
This is just one of many new initiatives being undertaken by traditional players, as well as new entrants, who recognise the potential for electrification and are willing to invest to make it feasible across all industry segments in compliance with global directives.
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