For the last eight years, engineers at Suncar AG, Zurich, Switzerland have been developing electric construction machines, and they offered some insights at the recent Future of Electrification 2024 conference, hosted by the Zapi Group. In a presentation titled “The all-electric construction machine,” Stefan Schneider, Suncar’s managing director, discussed progress on the road to electrification and the challenges of next-level electric machines.
Construction machinery, in essence, exists to perform work, run reliably as long as possible, and earn money for equipment owners, said Schneider. To succeed, electric vehicles need to be economically viable. They offer some advantages in terms of fuel costs and lower maintenance, compared to conventional machines, but there are hurdles as well. Nonetheless, more and more manufacturers are looking to make the shift from combustion engines to renewable drive trains, he said.
Suncar engineers have tested different approaches, including hybrid systems and fuel cells, and they’ve concluded the battery electric system is the best option. It’s robust and is suitable for machines ranging from micro excavators to crawler cranes which can lift over 200 tons.
But battery capacity also needs to be as small as possible because it’s the most expensive part of a machine, said Schneider. Therefore, designers are seeking intelligent solutions that let the batteries power an application for a full day.
To develop a zero-emission machine, engineers need to consider all the technical challenges, for example the battery size and capacity, the needed operation time, and the available charging infrastructure and charging systems. And examine additional efficiency improvements can be made to the machine so that these goals can be achieved, said Schneider. It’s also important to talk about economics in terms of fuel prices, and the price and source of electricity. Both can have a big influence on the environmental impact of such applications.
Another consideration is the different levels of electric machine design. Level one is the electrohydraulic machine. In essence, just replacing the diesel engine and installing an electric engine with batteries, chargers.
The next step, level two, will be optimizing the hydraulics or even replacing some hydraulic rotary drives with direct electric, because rotary drives are easy to electrify. However, linear actions would, for the most part, remain hydraulic cylinders.
Level three would install electromechanical linear actuators instead of hydraulic cylinders, but that possibility is probably five to 10 years in the future, said Schneider.
How does a zero-emission system actually work? As an example, a Suncar level-one 8.5 ton excavator has a 700-V system architecture, runs a four-hour shift hour two times a day with a dc fast charging cycle of one hour. It also offers an onboard ac connection that lets the machine recharge in 2.5 hours, and a grid connection that enables 24/7 operation.
The diesel engine and fuel tanks have been replaced with the battery system, onboard chargers, converters, and other electrical components. That’s a completely new system layout but, on level one, it retains the original hydraulics. That’s important to ensure a reliable machine, with the operator feeling just small differences versus a diesel machine, he said.
With growing experience, we’re seeing the potential to optimize, re-dimension, cost reduce, and enhance performance. Data is driving how battery lifetime has changed and machine efficiency has improved over the last few years. In addition, we also electrified the slewing drive for larger vehicles, recovering the rotation energy, and we’re now implementing the technology into smaller machines, he added.
Suncar engineers are looking to optimize the hydraulics, too. The stick and bucket motions are suitable for innovative pump solutions. And the boom, the most intense drive line in terms of energy consumption, offers high recuperation potential. Currently, the typical system works against pressure to lower the boom. Converting the boom drive to an electrohydraulic linear drive makes energy recovery possible, through a separate electric drive line, electric motor and pump. Overall, the aim is to improve machine efficiency with a defined goal of 35% more operation time available for the same applications with just these improvements.
There are challenges, too, said Schneider. There are the technical hurdles of dealing with high voltage systems. There are challenges involving road safety and braking systems with functional safety on the controllers and drive lines. In addition, we have space constraints. Electric motors are more compact than a combustion engine, but definitely larger than hydraulic propulsion. Hydraulic motors are renowned for being small with high power density. In addition, power electronics are additional devices that must be installed. It’s a challenge to make enough space available and handle the additional weight. “That’s definitely something which is not so easy to solve,” said Schneider.
“But an electric motor has the huge potential of minimizing mechanical losses using recuperation to having energy taken back which is otherwise just polluted through heat to the environment. We are seeing some first test results on diesel machines that have a potential of saving 30% of energy throughout the slew drive and around 30% of energy driving throughout the traction drives.
“We already estimated some efficiency improvements of the overall machine. But very critically and important in all these discussions is how the machine will be used. There is no standard application where the machine is used always in the same way, and it’s hard to define how consumption and efficiency improvements work for an individual customer. In some specific operation cycles such as leveling or grading, we have even estimated more than 75% lower energy consumption.”
What will be the future? That will be direct electric without any hydraulics, he said. In 10 to 20 years we will definitely see that machines will be electric because it enables autonomy or ease the way to implement different autonomy system. We are also seeing the benefit of AR technologies and teleoperation to run different machines on different construction sites from one office.
That also brings significant hurdles, he admits. “One challenge is that these linear actuators are bigger than hydraulic cylinders and that’s critical in terms of a good visibility,” said Schneider. These drive lines are subject to damage, for example, bucket actuators are near dangerous working areas where stones and rocks can cause critical components to fail.
Such installations also have high-voltage electrical cables mounted up front, which is definitely a challenge. In the end, engineers probably will need to limit flexibility a bit, depending on the arm layout, dimensions, and the freedom to reach every point as previously possible. And electrical linear actuators and motors face reliability challenges due to vibration and shock loads, which will need to be overcome.
Nonetheless, if we’re enabling more and more efficiency improvements, we can step-by-step improve to a point where we’re using 40% less energy which we input into the machine. And if we move to direct electric with no hydraulics, we’re probably saving 65% of input energy, he said.
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Filed Under: Electrification, Mobile Hydraulics - EV Engineering