Closed-loop hydraulic displacement control systems like EHAs (Electro Hydrostatic Actuators) can improve energy efficiency when compared to traditional metering valve-controlled systems, for example via the elimination of throttling losses.
Domin’s advanced additive manufacturing techniques enable miniaturisation while also allowing for the design of optimised fluid flow channels to improve flow efficiencies. The implementation of smart digital control systems can further optimise overall system performance. This blog will discuss the fundamentals of closed-loop hydraulic systems and how Domin’s solutions help reduce overall system energy losses.
What Are Closed-Loop Hydraulic Systems?
Closed-loop hydraulic systems are systems in which the hydraulic oil is recycled between the pump and motors or actuators within a pressurised network. Closed-loop systems are well suited to high-pressure applications like those found in aerospace or the automotive industry, as they generally have fast response times and can precisely position actuators. Closed-loop systems produce more heat because the oil is never returned to the large volume of a reservoir, where it can cool down. This is why closed-loop systems often require heat exchangers. Closed-loop hydraulic systems also have an oil reservoir, but it is significantly smaller than that used for open-loop systems. A typical example of a closed loop system is an EHA, i.e. electro hydrostatic actuator that includes all the required components in one package.
An open-loop system, in contrast, recycles the hydraulic oil back to a reservoir: the pump draws from the reservoir, and the motor/hydraulic cylinder discharges into the reservoir. Open-loop systems are often used for systems that require multiple actuators, such as those found in industrial automation applications.
What are the Benefits of Closed-Loop Hydraulic Systems?
Closed-loop hydraulic systems are most often used for flight controllers, vehicle suspension, and mobile equipment, for example, farming implements. This is due to their key benefits, as described below:
Lightweight and Compact
Existing closed-loop systems are often considered to be lighter than open-loop systems due to the removal of pipes, hoses, and throttling valves. However, it is often argued that closed loop systems can still be relatively heavy. Domin’s range of equipment makes extensive use of additive manufacturing as a core technology and can, therefore, make significant weight and size reductions when compared to standard closed loop systems. This reduced weight makes these systems ideal for mobile applications, where decreased mass translates directly to increased fuel efficiency or battery downsizing for electrified solutions.
Precision Control
The flow rate in a closed-loop system is controlled by the displacement setting in a variable displacement pump or by the speed in a fixed displacement pump. This method of flow control results in precise actuator control, through the dynamic variation of the swashplate angle or motor speed. In most cases, however, closed loop systems do not always provide the same level of precision as valve-controlled open loop systems. Domin’s range of equipment incorporates digital systems to optimise control and is designed with precision in mind to provide improved closed loop precision.
Reduced Equipment Costs
Closed-loop hydraulics systems do not require large oil reservoirs and also do not need as much hydraulic oil to operate effectively. In addition to this, directional control can be achieved by directly controlling the pump, without the need for the separate direction-control valve required for an open-loop system.
Energy Savings
Domin lays the foundation for high hydraulic system energy efficiency by designing valves with significantly reduced flow restriction. Furthermore, Domin’s closed loop systems are designed to be as lightweight as possible, which directly translates to improved fuel efficiency in automotive or aerospace applications. Closed loop systems also benefit from nearly throttle-free control which helps improve energy efficiency by limiting throttling losses.
Closed-loop hydraulic systems can be designed with regenerative capabilities to harvest energy that is otherwise wasted during braking, for example. During braking, kinetic energy is transferred to an accumulator via the hydraulic pump and stored as pressure, when accelerating, this pressure from the accumulator is released. This effect can be used to improve system efficiency. This method of energy recovery is significantly more challenging and less effective in open-loop systems.
Improved Hydraulic Efficiency with Domin Systems
When designing a hydraulic loop, it is important to understand the key performance requirements. At Domin, we provide hydraulic system solutions to the automotive, industrial, and aerospace industries. To learn more about how we can help your hydraulic systems achieve significant increases in efficiency, contact a Domin representative today.
