Recently, Parker Hannifin’s Hydraulic Pump and Power Systems engineers offered a webinar to the OEM Off-Highway readers describing the conversion process from an Internal Combustion Engine (ICE) powered hydraulic system to an electrically powered one.
Here is a recap:
Increased RPM
Increased RPM is a significant factor for OEMs and end-users to consider when moving to electric power. Permanent magnet electric motors can run at much higher speeds than what a hydraulic pump is subjected to when powered by ICE. Plus, they can accelerate and decelerate very quickly and be turned on and off to save energy.
But more than just speed needs to be considered. Overall hydraulic component performance must be evaluated. For example, cavitation concerns, longevity, or maintenance issues could now occur. Correctly matching the hydraulic pump, electric motor, and inverter in electrified work functions is critical to transitioning to a fully electrified system. Unique operating conditions of any application will also factor into the transition. Extensive testing of components in the system against all these factors can assure system performance and the life of the pump.
Size
Because electrified systems can spin faster, you can downsize the hydraulics, which will impact the overall size of the hydraulic system versus a traditional internal combustion engine (ICE) system.
Noise
Noise can be a factor after the ICE is removed from the system. The hydraulics or the work function tends to become the loudest part of the application.
Cost
Key considerations are component cost and total cost of ownership (TCO) for the life of the product. For example, more energy-efficient solutions will require a higher up-front investment, but future energy savings will likely offset the higher cost.
Robustness
The pump's life must be aligned with the end user’s expectations.
System Complexity
Understanding all the nuances for the specific electro-hydraulic unit, whether that is displacement control, different cooling loops, etc.
Efficiency
Hydraulic efficiency has always been a high priority in design, but not always the top priority. With battery power being crucial to electro-hydraulic systems, efficiency is a key consideration when determining either battery sizing or runtime.
Available Hydraulic System Architectures and The Pros and Cons of Each
Internal Combustion Engine (ICE) Centralized Architecture
Today, most equipment has either gas or diesel-powered ICE. ICE units have continuous high idle of around 2000 rpm and are sized for the peak power requirement for both work function and driving traction needs. From the work function perspective, these systems have one pump that supports all its functions.
The advantage of the ICE centralized architecture is that it is a proven, robust system with plenty of economical hardware choices. In addition, the ICE architecture has been unchanged for decades, so the industry is highly familiar with it.
The ICE system's cons are the compounding hydraulic and combustion engine losses (such as exhaust and noise) that add to inefficiencies. Couple that with government regulations driving the need to move to a carbon-free energy source, like electricity, and the trend to move away from this type of architecture increases.
Electrically Powered Centralized Architecture.
Another type of architecture that is a good fit for future electric power is a centralized architecture with an electric motor drive. One benefit of this system is the ability to share a significant amount of the existing work function through your valves, cylinders, and hoses. While you cannot simply remove a diesel engine and replace it with an electric motor, and system analysis is required, you can still reuse a lot of your work function system.
A centralized electric pump commonly powers these types of systems. Permanent magnet AC motors can spin from 0 RPM during a shutdown case to up to 8,000 RPM. In some cases, you can fully decouple the traction and work circuits so that when one circuit is not needed, the unused system can be shut off to increase the power of the other. For example, when the traction circuit is not needed, all the power can be used by the work circuit.
This system’s purpose is to provide better energy input with more efficient outputs. This is achieved by using your electric motor’s controls and finding optimum shaft speeds of pumps and motors to reduce system losses.
One disadvantage of this system is that the inefficiencies of a centrally powered system still exist. Pump and valve losses and the need to cool the hydraulic circuit will still occur. With that said, the electrically powered centralized architecture is still a good compromise between a traditional ICE and a fully electric-powered system.
Electrically Powered Decentralized Architecture
The most efficient architecture option moving forward is a decentralized electrically powered architecture.
The architecture with multiple point-of-use electrohydraulic pumps, electric motors, and hydraulic motors located at the actual load where power is required provides significant efficiency gains, as well as opportunities for better matching the electrohydraulic pumps with the requirements of working circuits they power.
This system includes the ability to regenerate energy and achieve overall better energy efficiency through cooling losses and the reduction of components, including pumps and valves. The top benefit is better system control and more ideal energy utilization.
The con, however, is that OEMs must consider a significant amount of hardware rework and changes to controls. In addition, the ability to turn on and off individual electrohydraulic actuators or pumps at each load will present a significant learning curve to all involved.
The advantages of a decentralized system
A decentralized system is more efficient than both an ICE system and an electrically powered centralized system. It provides point-of-use power, and each component can be optimized for its specific task rather than sharing requirements with a single pump. Decentralizing these systems also allows for reductions in the line, pumping, and relief losses, which can reduce the amount of non-value-added work.
In addition to improving or optimizing system efficiency, a decentralized system can provide longer battery life. For example, if a full battery electric system is needed, reducing or regenerating energy like a hybrid or fully electric car can be achieved with a decentralized system.
Depending on the load cycle, a decentralized system can dramatically improve the battery life, and reduce the need for larger batteries or the quantity of batteries used on equipment.
Finally, a decentralized system offers separate shut-off systems, allowing the ability to turn off any function when not in use, resulting in less energy waste and greater overall system efficiency.
You can view the webinar here: How To Take a Calculated Leap to an Electrified System with Electro-Hydraulic Pumps (parker.com)
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