Electro-Hydraulic Actuators vs Hydraulics

Electro-hydraulic actuators can offer a more efficient and serviceable alternative to large conventional hydraulic systems in the right off-highway applications. Hydraulics have powered construction and agricultural machinery for decades, but they bring a familiar set of drawbacks: chronic leaks, hot oil, noisy pumps, drifting cylinders and baked‑in efficiency losses. In a world of battery‑electric and hydrogen powertrains, tighter environmental rules and rising operating costs, those compromises start to look like the weak link in the system.

A more modern approach is to treat electric linear actuators and compact electro‑hydraulic actuators (EHAs) as the default, and reserve large central hydraulic systems for the few places where they are genuinely the best tool for the job.

The problem with traditional hydraulics

A conventional hydraulic system takes mechanical power from an engine or motor, converts it to fluid power, pushes that through hoses and valves, then converts it back to mechanical force at a cylinder. Each step wastes energy as heat, pressure drop and leakage, so overall efficiency for a full hydraulic circuit is often closer to 40–55% than to 100%.

In practice that means:

Pumps circulating oil at pressure even when nothing is moving, just to stay “ready”.
Extra coolers, fans, filters and plumbing to deal with the heat and contamination that system creates.
Numerous potential leak points at hoses, fittings and seals, with associated spill risk and clean‑up costs.
Drift and compliance that make tight control and automation harder.

On diesel machines this could be hidden behind a big fuel tank and a cheap kilowatt. On zero‑emission platforms, every wasted watt‑hour either shortens runtime or forces you into bigger, more expensive batteries or fuel cells.

A lot of this only really hits home when you try to electrify an existing hydraulic platform. On one 7.5‑tonne machine, the diesel engine was swapped for a 100 kW electric motor and lithium‑ion battery pack, but the hydraulics were left largely unchanged: a hydrostatic drive with a variable‑displacement pump and separate gear pumps for lift and steer. On paper the new motor exceeded the old 75 kW diesel; in practice, battery life was poor and both the motor and inverter ran hot because the system spent much of its time in inefficient parts of the pump and motor maps rather than at a sensible operating point. When the main pump was resized from 43 cc/rev down to 28 cc/rev and the control strategy adjusted, the drive motor finally sat in its “sweet spot” and the thermal issues eased – but the experience underlined the root problem: simply swapping the prime mover without re‑thinking the hydraulic architecture is a sticking‑plaster, not a solution. In retrospect, that machine would have been a strong candidate for electric wheel or hub drives and a much smaller, more tightly scoped hydraulic system rather than trying to drag a legacy hydrostatic package into an electric future.

Where electric linear actuators make more sense

Electric linear actuators convert electrical power directly into linear motion via a motor and screw or similar mechanism, with no central oil circuit. Modern designs routinely hit 75–80% efficiency and higher, roughly double what a full hydraulic circuit manages.

Compared with hydraulics, they offer:

Power on demand – meaningful energy draw only when you command movement, not to hold static pressure.
Built‑in precision – integrated position and load feedback make closed‑loop control, repeatable positioning and safe automation much more straightforward.
Clean and quiet operation – no hydraulic oil, minimal external plumbing and significantly lower noise levels.
Simpler maintenance – no hose chasing, oil sampling or filter changes; service regimes look like electric drive maintenance, not fluid power troubleshooting.

For a growing set of tasks – stabilisers, hatches, secondary booms, attachment couplers, control surfaces – electric actuators now comfortably deliver the required forces and strokes, particularly as high‑force industrial units aimed at off‑highway use become more common.

Where electro‑hydraulic actuators still earn their keep

There are still functions where you need a hydraulic cylinder’s force density and robustness, but don’t want a machine‑wide oil system. Electro‑hydraulic actuators (EHAs) solve that by keeping a small hydraulic circuit local to each function.

A typical EHA is a sealed package: cylinder, pump, valves and sensors driven by an electric motor. To the machine, it looks like a smart actuator on the power and communications buses; all the oil stays inside the unit.

That brings some useful advantages:

Localising any leaks or failures to one function instead of a shared circuit.
Eliminating long hose runs and central manifolds, shrinking total oil volume and leak paths.
Letting high‑force functions plug straight into an electric or hydrogen powertrain without dragging a full hydraulic system along for the ride.

There is also a mechanical reason to keep hydraulics in the loop for certain jobs: controlled compliance. Steel links and high‑stiffness electric actuators will faithfully transmit whatever shock the structure sees; a well‑designed hydraulic stage gives you a small but vital amount of “squish” to soak up curb strikes, potholes and sudden load shifts that can easily reach 8–10 g in real off‑highway duty. In sway stabilisers and steering gear, that inherent hydraulic give can act as a mechanical fuse and shock absorber, protecting pins, frames and operators from the worst of these transients. EHAs let you retain that behaviour, but wrap it in sensors and control logic so the machine still sees a smart, fully controllable actuator rather than a passive oil‑filled ram.

Why this aligns with zero‑emission powertrains

Once the prime mover is electric or hydrogen, the priorities downstream become efficiency, controllability, noise and environmental risk:

Efficiency and runtime – more efficient actuators directly translate into longer runtimes or smaller batteries and fuel cells for the same work done.
Smarter control – electric and electro‑hydraulic actuators speak the same language as modern controllers, making it much easier to implement features like active levelling, adaptive damping and load‑aware assistance.
Noise and neighbourhood impact – removing or shrinking hydraulic powerpacks cuts major noise sources, which matters on urban and extended‑hours sites.
Spill reduction – less oil in fewer places reduces the risk and cost of leaks, which is increasingly important as clients and regulators tighten expectations around clean sites.

In short, if you are investing in a zero‑emission powertrain, leaving a large, lossy hydraulic system bolted on the side undermines much of the benefit.

A pragmatic path forward

This is not about banning hydraulics at all costs. It is about being deliberate:

Default to electric linear actuators where the force, stroke and duty cycle allow it.
Use sealed, serviceable EHAs where high forces and harsh loading demand hydraulic muscle, but keep that oil local and under control.
Avoid specifying large central hydraulic systems on new electric or hydrogen machines unless there is a clear, quantified reason they outperform the alternatives.

That shift replaces a lot of “dumb steel and oil” with high‑fidelity, instrumented actuators that the control system can understand, protect and use more intelligently. It improves efficiency and reliability today, and opens the door to the kind of active stability, safety and automation features that will be expected of off‑highway machines over the next decade.