ISO 22072:2005

INTERNATIONAL ISO
STANDARD 22072
First edition
2005-06-01

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 22072:2005(E)
©
ISO 2005

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ISO 22072:2005(E)
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ISO 22072:2005(E)
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.


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INTERNATIONAL STANDARD ISO 22072:2005(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 servocontrol actuators that are currently
used. It is intended that this International Standard cover the unique requirements of EHAs.
Test methods are defined in a separate ISO document.
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
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
electrohydrostatic actuator
EHA
electrically powered actuator that includes one or several hydraulic rams whose chambers are connected to a
bi-directional, fixed-displacement pump driven by a variable-shaft-speed, electric motor controlled by power
electronics
NOTE 1 A typical arrangement includes an integrated hydraulic fluid compensator, a manifold that interconnects the
above hydraulic elements and in which components necessary for additional functions can be installed, see Figure 1.
NOTE 2 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 3 This assembly may also perform other functions, 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.
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ISO 22072:2005(E)

Key
1 command signal
2 power supply
3 power electronics
4 electric motor
5 fluid compensator
6 pump
7 position transducer signal
8 check valve (2 places)
Figure 1 — Typical arrangement of an electrohydrostatic actuator
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,
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ISO 22072:2005(E)
 filling,
 draining,
 bleeding,
 internal fluid filtering,
 no-back,
 local dissipation of generated energy,
 force or speed limitation,
 stops,
 temperature monitoring,
 heating of stand-by unit.
4.3.2 Mechanical interface
The specification drawing shall define the following:
 allocated space envelope;
 dimensions and tolerances of the mechanical connections or the dimensional standards if connections
are achieved through standardized components;
 line replaceable units (LRUs);
 access once installed on aircraft;
 specific items such as hoisting or jack catcher interfaces, as required.
4.3.3 Electrical interface
The electrical interface definition 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 LRUs;
 segregation rules to comply with;
 descriptions of signals exchanged, definition of input and output impedances;
 power interruption capability and definition of the strategy for longer interruptions (see 5.3).
4.3.4 Hydraulic interface
The hydraulic interface requirements shall include definition and location of possible filling, bleeding, filtering
and draining features.
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ISO 22072:2005(E)
4.3.5 Software
Software may be used to achieve various functions, such as
 electric motor control,
 loop closure,
 monitoring and redundancy management,
 status information,
 built-in test.
The level of criticality and of the associated development, verification, and validation methods shall be
specified. Memory capacity extension and processing power shall be specified. If required, dissimilarity in
processing/software/compilers/electronic hardware shall be specified.
4.4 Performance
4.4.1 Mechanical performance
The definition of the requirements for output force or mechanical power shall take into account the thermal
behaviour. These mechanical requirements shall therefore be associated with their duration and
environmental conditions. Thus the following shall be specified.
 Maximum operating output force: the maximum driving force to be generated by the unit at very low
speed (to be defined), for a short time duration (to be defined), under specified supply and environmental
conditions, and the associated tolerances.
 Maximum continuous output force: the maximum holding force, with no movement, or the maximum
driving force, at very low speed (to be defined), to be generated under given supply and environmental
conditions with no time limitation, with and without its possible no-back device engaged, and the
associated tolerances.
 ‘Worst case’ scenarios: operational sequences, or series of sequences, described as functions of time in
terms of position, force, environmental conditions, identified as sizing cases in terms of the instantaneous
power absorbed or rejected, or in terms of heat generated. Force fighting shall be considered, depending
on system configuration.
 Maximum rate and associated loading conditions, or expressed as the time necessary to reach a given
position under a specified load. The rate versus load characteristic shall be identified.
 Run-up time: time from activation of stand-by actuator to being able to achieve maximum rate with a
maximum rate demand.
 Dynamic performance as specified below may also be a sizing consideration.
 Working stroke, stop to stop stroke.
 Possible acceptable temporary degradation of performance at start up, following cold soak in particular.
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