Electro-hydraulic actuator

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Electro-hydraulic actuator (EHA)

What is an EHA
An electro-hydraulic actuator is a self-contained unit that uses electricity to run its own hydraulic pump. It replaces the need for a separate hydraulic pump and long tubing, making the system simpler, lighter, and more reliable. EHAs were first developed for aerospace and have since found use in many industries that use hydraulic power.

How it works
- A compact high-power motor inside the unit drives a pump that pressurizes hydraulic oil.
- This pressure moves a hydraulic cylinder, which provides the actuation.
- The entire pump, cylinder, and fluid reservoir are packaged together in one unit.
- Electrical signals control the pump speed (often with pulse-code modulation), so energy and control travel over a single set of wires. This is known as a power-by-wire system.

Advantages
- Fewer external parts: no separate hydraulic supply or extensive piping.
- Weight and space savings, with simpler, more streamlined installation.
- Internal pressure is maintained, so the system isn’t constantly drawing power when not moving.
- Power is used only when the actuator is moving, reducing overall power consumption.
- Redundancy can be achieved by using two EHAs per surface, plus two sets of wiring.

Conventional designs and context
- In older aircraft, hydraulics used engine-driven pumps and cables to control surfaces, with valves and external hydraulics.
- As aircraft grew, fly-by-wire and other electronic control methods were developed, adding complexity. EHAs offer a self-contained alternative that reduces the need for separate hydraulic systems.

EHAs in practice
- EHAs combine a high-power motor, a reversible pump, and a hydraulic cylinder in one package.
- They operate with electrical power and control signals over the same wiring, creating a true power-by-wire solution.
- This approach can reduce weight, improve safety, and simplify maintenance compared to traditional hydraulic systems.

Things to consider
- EHAs rely on reliable electrical power and electronics.
- Thermal management and proper control design are important for performance and safety.
- While simpler than traditional hydraulics, EHAs still require careful engineering, especially for redundancy and safety-critical applications.