ISO 22072:2011

INTERNATIONAL ISO
STANDARD 22072
Second edition
2011-08-01
Aerospace — Electrohydrostatic actuator
(EHA) — Characteristics to be defined in
procurement specifications
Aéronautique et espace — Actionneurs électrohydrostatiques (EHA) —
Caractéristiques à définir dans les spécifications d'approvisionnement

Reference number
©
ISO 2011
©  ISO 2011
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ii © ISO 2011 – All rights reserved

Contents Page
Foreword . iv
Introduction . v
1  Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  Requirements . 3
4.1  General . 3
4.2  Brief description of the system . 3
4.3  Description and interfaces . 3
4.4  Performance . 4
4.5  Electrical power consumption and regeneration . 6
4.6  Hydraulic consumption . 7
4.7  Strength and life . 7
4.8  Protection against fire risk . 7
4.9  Reliability and safety . 8
4.10  Bonding . 8
4.11  Lightning, electromagnetic compatibility . 8
4.12  Maintainability and servicing . 8
4.13  Thermal requirements . 9
5  Installation and operating conditions . 9
5.1  General . 9
5.2  Mechanical data . 9
5.3  Electrical supply data . 9
5.4  Thermal data . 9
5.5  Hydraulic data . 10
5.6  Control and monitoring data . 10
5.7  Environmental data . 10
5.8  Duty cycle data . 10
Bibliography . 12

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 22072 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 10, Aerospace fluid systems and components.
This second edition cancels and replaces the first edition (ISO 22072:2005), which has been technically
revised. This second edition adds requirements for electronic module hardware (4.3.5), operation under failure
conditions (4.4.5), electrical power consumption and regeneration (4.5) and fatigue wear life (4.7.2).

iv © ISO 2011 – All rights reserved

Introduction
Electrohydrostatic actuators (EHAs) are integrated, electrically powered, hydraulic actuators that are used to
power aircraft control surfaces or other moving parts.
This International Standard provides requirements that should be included in a Procurement Specification for
this type of actuator.
INTERNATIONAL STANDARD ISO 22072:2011(E)

Aerospace — Electrohydrostatic actuator (EHA) —
Characteristics to be defined in procurement specifications
1 Scope
This International Standard defines the general characteristics, requirements and design data to be included
in the procurement technical specification of an electrohydrostatic actuator (EHA) to be used to power aircraft
control surfaces or other moving parts of an aerospace vehicle.
This type of actuator is an alternative to the hydraulically powered servo-control actuators that are currently
used. It is intended that this International Standard cover the unique requirements of EHAs.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 7137, Aircraft — Environmental conditions and test procedures for airborne equipment
1)
DO-178B, Software Considerations in Airborne Systems and Equipment Certification
1)
DO-254, Design Assurance Guidance for Airborne Electronic Hardware
SAE ARP1383B, Impulse Testing of Aerospace Hydraulic Actuators, Valves, Pressure Containers, and Similar
2)
Fluid System Components
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
electrohydrostatic actuator
EHA
an electrically powered actuator that includes one or several hydraulic rams
NOTE 1 The chambers of each ram are connected to an integrated hydraulic fluid reservoir and to a bidirectional,
fixed-displacement pump driven by a variable-shaft-speed, bidirectional electric motor controlled by an electronic module
including power electronics, mounted on the actuator or remotely, and considered a part of the actuator.
NOTE 2 The motor/pump/power electronics assembly may be incorporated into a standard Electrohydrostatic Module
(EHM).
1) RTCA – Radio Technical Commission for Aeronautics, www.rtca.org.
2) SAE – Society of Automobile Engineers, www.sae.org.
NOTE 3 A manifold, in which components necessary for additional functions can be installed, interconnects the
mechanical elements; see Figure 1. The additional functions may include, for example, allowing the operation of other
actuators installed in parallel, or ensuring the damping of movement of the load in case of loss of all electric power.
NOTE 4 This assembly is part of the position control loop of the surface, or of any other load, in which the error signal,
difference between the commanded and achieved positions determines the command of the speed and direction of
rotation of the motor. Other components of the position servo-loop, e.g. position transducer, control electronics, generating
the error signal and control laws, do not necessarily form part of this assembly.
NOTE 5 The electronic module function may be limited to Motor Drive Electronics (MDE), higher-level functions such
as closing the position loop, control laws, failure detection and isolation, and built-in-test being implemented in a central
computer, or these functions can be included as an Electronics Control Unit (ECU).

Key
1 command signal 7 position transducer signal
2 power supply 8 anti-cavitation check valve (two places)
3 electronic module 9 piston
4 electric motor 10 EHM
5 reservoir 11 filling port
6 pump
Figure 1 — Typical arrangement of an electrohydrostatic actuator
3.2
digital signal processor
DSP
integrated circuit designed for processing signals by digital means as opposed to analogue means
3.3
field-programmable gate array
FPGA
integrated circuit designed to be configured by the designer or user after manufacturing
2 © ISO 2011 – All rights reserved

4 Requirements
4.1 General
The requirements defined in 4.2 to 4.13 shall be met under all rated operating conditions and during the
service life specified.
4.2 Brief description of the system
The EHA is one component of a system. The various configurations or reconfigurations typical of this system
involve specific modes of EHA operation which shall be described. Normal and failure modes of operation for
the EHA shall be defined.
4.3 Description and interfaces
4.3.1 General description
The unit shall be described in terms of functions and the associated terminology defined.
The following are examples:
 control/electrical/mechanical/structural redundancy;
 local or remote fluid level indication/monitoring;
 filling, either from a ground support equipment or a central hydraulic system;
 draining;
 bleeding;
 internal fluid filtering;
 anti-back-driving device;
 local dissipation of generated energy;
 force and/or pressure and/or speed limitation;
 stops;
 temperature monitoring;
 heating of stand-by unit; etc.
4.3.2 Mechanical interface
The specification, or a separate interface control document, shall define:
 allocated space envelope;
 dimensions and tolerances of the mechanical connections or the dimensional standards if connections
are achieved through standardized components;
 line replaceable units;
 access once installed on aircraft;
 interfaces with specific items (such as hoisting devices or “jack catchers”) intended to hold the unit in
place in the event of attachment rupture or disconnection, to avoid secondary damage to surrounding
structures or equipment, etc., as required.
4.3.3 Electrical interface
The specification, or a separate interface control document, shall include:
 wiring schematics defining the electrical connections with power supply, control and monitoring systems,
standards, sizes and pin allocation of interface connectors;
 any particular requirements or limitation on use of connectors for the line replaceable units;
 segregation rules to comply with, including signal separation requirements;
 descriptions of signals exchanged, definition of input and output impedances;
 power interruption capability and definition of the strategy for longer interruptions (see 5.3);
 bonding interface;
 shielding requirements;
 specific insulation requirements associated with the use of high voltage d.c.
4.3.4 Hydraulic interface
The hydraulic interface requirements shall include definition and location of possible filling, bleeding, filtering
and draining features.
4.3.5 Electronic module hardware, software/firmware
Various control and monitoring functions, such as listed below, can be implemented locally in the embedded
electronic module, which is primarily intended to host the motor drive electronics, or shared with central
computers:
 loop closure;
 monitoring and redundancy management;
 status information;
 built-in test;
 allowable type of processor such as DSP or FPGA may be specified; etc.
The level of criticality and of the associated development, verification and validation methods, configuration
control, applicable to the software and firmware shall be specified with reference to DO-178B and DO-254.
Memory capacity extension and processing power shall be specified.
Implementation of monitoring functions may require physical segregation, independent hard
...