The push to electrify non-road mobile machinery is gathering pace, driven by tightening emissions regulations and the rising cost of diesel-powered fleets. Yet even as electric motors and batteries replace internal combustion engines, electrohydraulic control systems remain central to how these machines actually move. Excavators, loaders and other off-highway vehicles still rely on hydraulics for their high power density and resistance to shock loads, which means the real opportunity lies in rethinking how electrohydraulic control systems are designed, matched and managed within an electrified powertrain.
Why Electrohydraulic Control Systems Still Matter
Despite electrification, hydraulic systems in non-road machinery typically only achieve average energy efficiencies of around 21%, largely due to losses from engine drive and valve throttling. Replacing the constant-speed internal combustion engine with a variable-speed electric motor changes this picture considerably. Under most operating conditions, machinery driven by electric motors can reach efficiencies between 43% and 71%, a substantial improvement that stems from better matching between the motor and the hydraulic pump. This is the first major opportunity for electrohydraulic control systems: pairing variable-speed motors with variable-displacement pumps allows both components to run closer to their high-efficiency zones, rather than the motor operating constantly at a fixed rated speed regardless of load.
Capturing Energy That Would Otherwise Be Wasted
A second opportunity comes from energy regeneration. Lifting, swinging and lowering movements, such as the boom motion of an excavator, generate kinetic and potential energy that traditional systems simply dissipate as heat. Electric energy recovery systems address this by using a hydraulic motor, an electric motor and a storage device, such as a battery or supercapacitor, to capture and reuse this energy. Reported recovery rates vary considerably depending on the configuration, from modest improvements through to figures as high as 82.7% of potential energy recycled in some boom-based designs. The trade-off is that more energy conversion steps tend to reduce overall recovery efficiency, so simplifying these intermediate stages remains an active area of development.
The Persistent Challenge of Controllability
Electro-hydraulic actuators offer a further step forward by decoupling electric control from power transmission entirely, removing the throttling losses associated with centralised pump circuits. However, this comes with genuine drawbacks. Removing the throttling valve reduces system stiffness, making dynamic response and positioning accuracy worse under sudden loads. Mode-switching oscillation is another recognised problem, where the spool position within flow-balancing valves becomes uncertain at critical load thresholds, causing pressure and velocity to fluctuate. Narrow speed-regulating ranges add to the difficulty, since most hydraulic pumps struggle to maintain good lubrication at low speeds. Various circuit redesigns, including multi-chamber cylinders and dual-pump arrangements, have been proposed to address these issues, though each tends to introduce additional cost, size or complexity.
Compactness and Power Density
For off-highway vehicles, where installation space is at a premium, compactness is a persistent constraint on electrohydraulic control systems. Two main approaches have emerged: integrating the pump and motor into a single unit, and increasing pump rotational speed to shrink component size. Some high-speed pumps have already reached speeds of 10,000 r/min or more in research and commercial settings, though displacement tends to fall as speed rises, limiting their suitability for larger machinery with high flow demands.
Looking Ahead
Electrification has not eliminated the relevance of hydraulics in off-highway vehicles; if anything, it has sharpened the need to optimise how electrohydraulic control systems are designed. The opportunities around efficiency, energy regeneration and operational flexibility are considerable, but they sit alongside real challenges in controllability, durability and compactness. Continued progress will likely depend on a combination of smarter circuit design, higher-performance components and more sophisticated energy management strategies tailored to the demanding, variable-load nature of non-road machinery.
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