ISO 22181:2021

Aerospace fluid systems and components — Variable displacement hydraulic motors — General specifications

This document establishes the general requirements for variable displacement uni-directional and bi-directional hydraulic motors, suitable for use in aircraft hydraulic systems at pressures up to 35 000 kPa (5 000 psi). These requirements include: — design requirements; — test requirements. Primary and secondary function motors (see Clause 4) are covered in this document; however, actuators with internal rotation angle limits and low-speed motors are not covered. This document is intended to be used in conjunction with the detail specification that is particular to each application.

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General Information

• Status: Published
• Publication Date: 08-Feb-2021
• ICS: 49.080 - Aerospace fluid systems and components
• Technical Committee: ISO/TC 20/SC 10 - Aerospace fluid systems and components
• Drafting Committee: ISO/TC 20/SC 10/WG 9 - Hydraulic power and actuation equipment
• Current Stage: 6060 - International Standard published
• Start Date: 09-Feb-2021
• Due Date: 31-Jan-2022
• Completion Date: 09-Feb-2021

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 22181
First edition
2021-02
Aerospace fluid systems and
components — Variable displacement
hydraulic motors — General
specifications
Reference number
©
ISO 2021
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii © ISO 2021 – All rights reserved

Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Classification . 7
5 General requirements . 7
5.1 Order of precedence . 7
5.2 Hydraulic system characteristics . 7
5.3 Airworthiness regulations . 8
5.4 Qualification . 8
6 Functional requirements . 8
6.1 Hydraulic fluid . 8
6.2 Pressures . 8
6.2.1 Rated supply pressure. 8
6.2.2 Rated differential pressure . 8
6.2.3 No-load break-out pressure . 8
6.2.4 Motor return port pressure . 9
6.2.5 Case drain pressure . 9
6.3 Flows . 9
6.3.1 Rated consumption . 9
6.3.2 Case drain flow . 9
6.3.3 Shaft seal leakage .10
6.3.4 External leakage .10
6.4 Speed and direction of rotation .10
6.4.1 Speed .10
6.5 Torque .11
6.5.1 Rated torque .11
6.5.2 Break-out torque .11
6.5.3 Stalling torque .11
6.5.4 Maximum stalling torque .11
6.5.5 Torque pulsations .11
6.6 Variable output load control .11
6.6.1 General.11
6.6.2 Response time .12
6.6.3 Stability .12
6.7 Motor overall efficiency .12
6.8 Dynamic characteristics .13
6.8.1 General.13
6.8.2 Dynamic braking .13
6.8.3 Rapid reversals .13
6.9 Passive operation .13
6.10 Fluid and ambient temperature .13
6.10.1 Fluid temperature .13
6.10.2 Ambient temperature .13
6.11 Acoustic noise level .14
6.12 Rated endurance .14
6.13 Environmental requirements .14
7 Detail design requirements .15
7.1 Dimensionally critical components .15
7.2 Maintainability features .15
7.3 Seals .15
7.4 Lubrication .15
7.5 Balance .15
7.6 Self-contained failure .16
7.7 Safety wire sealing .16
7.8 Electro-conductive bonding .16
7.9 Marking .16
7.9.1 Nameplate .16
7.9.2 Modification standard .16
7.9.3 Fluid identification .16
7.9.4 Ports .16
8 Strength requirements .17
8.1 General .17
8.2 Proof pressure .17
8.2.1 Motor case .17
8.2.2 Motor inlet port .17
8.2.3 Motor return port .17
8.3 Ultimate pressure .17
8.3.1 Motor case .17
8.3.2 Motor inlet port .17
8.3.3 Motor return port .17
8.4 Pressure impulse (fatigue) .17
8.5 Port strength .18
9 Construction requirements .18
9.1 Materials .18
9.1.1 General.18
9.1.2 Metals .18
9.2 Corrosion protection .18
9.2.1 General.18
9.2.2 Ferrous and copper alloys .19
9.2.3 Aluminium alloys .19
9.3 Castings .19
10 Installation requirements.19
10.1 Dimensions .19
10.2 Mass .19
10.3 Mounting .20
10.4 Orientation .20
10.5 Drive shaft .20
10.6 Ports .20
11 Maintenance requirements .21
11.1 Maintenance concept .21
11.2 Service life limitations and storage specifications .21
12 Reliability requirements .21
12.1 Equipment compliance .21
12.2 Requirements .21
13 Quality assurance provisions .21
13.1 Responsibility for inspection .21
13.2 Classification of tests .21
13.3 Test stand requirements .22
14 Acceptance tests .22
14.1 General .22
14.2 Examination of the product .22
14.3 Test programme .23
14.3.1 General.23
14.3.2 External leakage requirements .23
14.3.3 Break-in run .23
iv © ISO 2021 – All rights reserved

14.3.4 Proof pressure and overspeed tests .23
14.3.5 Operational tests at rated conditions .24
14.3.6 Break-out torque test .24
14.3.7 Teardown inspection examination .24
14.3.8 Run-in .25
14.3.9 Speed control test .25
14.3.10 Performance data .25
14.3.11 Fluid contamination test .26
14.4 Storage and packaging .27
15 Qualification procedures .27
15.1 General .27
15.2 Qualification procedure .27
15.2.1 Qualification by analogy .27
15.2.2 Motor qualification test report .27
15.2.3 Samples and program of qualification tests .27
15.3 Qualification testing .28
15.3.1 Dimensional check .28
15.3.2 Expanded envelope acceptance tests .28
15.3.3 Overspeed test .28
15.3.4 Operational test at overpressure .29
15.3.5 Calibration .29
15.3.6 Endurance testing .31
15.3.7 Environmental tests .34
15.3.8 Structural tests .35
15.3.9 Combination tests .37
15.3.10 Supplementary tests .37
Bibliography .38
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 10, Aerospace fluid systems and components.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
vi © ISO 2021 – All rights reserved

Introduction
It is noted that, while ISO standards refer to SI units, large segments of the aerospace industry refer
to other measurement systems as a matter of common working practice. All dimensions used in this
document are in SI units with the non-SI units given in addition for the convenience of those users more
familiar with these.
It is further noted that the standard ISO decimal symbol “,” (comma) is not used as common working
practice for inch dimensions. A decimal point is used in the inch dimensions in this document as in
many other aerospace standards.
NOTE The use of non-SI units and the decimal point in this document does not constitute general acceptance
of measurement systems other than SI within International Standards.
INTERNATIONAL STANDARD ISO 22181:2021(E)
Aerospace fluid systems and components — Variable
displacement hydraulic motors — General specifications
1 Scope
This document establishes the general requirements for variable displacement uni-directional and
bi-directional hydraulic motors, suitable for use in aircraft hydraulic systems at pressures up to
35 000 kPa (5 000 psi).
These requirements include:
— design requirements;
— test requirements.
Primary and secondary function motors (see Clause 4) are covered in this document; however, actuators
with internal rotation angle limits and low-speed motors are not covered.
This document is intended to be used in conjunction with the detail specification that is particular to
each application.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 2093, Electroplated coatings of tin — Specification and test methods
ISO 2669, Environmental tests for aircraft equipment — Steady-state acceleration
ISO 2671, Environmental tests for aircraft equipment — Part 3.4 : Acoustic vibration
ISO 2685, Aircraft — Environmental test procedure for airborne equipment — Resistance to fire in
designated fire zones
ISO 3323, Aircraft — Hydraulic components — Marking to indicate fluid for which component is approved
ISO 3601-1, Fluid power systems — O-rings — Part 1: Inside diameters, cross-sections, tolerances and
designation codes
ISO 7137, Aircraft — Environmental conditions and test procedures for airborne equipment
ISO 7320, Aerospace — Couplings, threaded and sealed, for fluid systems — Dimensions
ISO 8078, Aerospace process — Anodic treatment of aluminium alloys — Sulfuric acid process, undyed coating
ISO 8079, Aerospace process — Anodic treatment of aluminium alloys — Sulfuric acid process, dyed coating
ISO 8399-1, Aerospace — Accessory drives and mounting flanges (Metric series) — Part 1: Design criteria
ISO 8399-2, Aerospace — Accessory drives and mounting flanges (Metric series) — Part 2: Dimensions
ISO 8625-1, Aerospace — Fluid systems — Vocabulary — Part 1: General terms and definitions related to
pressure
ISO 8625-2, Aerospace — Fluid systems — Vocabulary — Part 2: General terms and definitions relating to
flow
ISO 8625-3, Aerospace — Fluid systems — Vocabulary — Part 3: General terms and definitions relating to
temperature
ISO 11218, Aerospace — Cleanliness classification for hydraulic fluids
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8625-1, ISO 8625-2, ISO 8625-3,
and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
variable displacement hydraulic motor
mechanical actuator that converts hydraulic pressure and flow into torque and angular velocity
(rotation) and whose speed is controlled by varying the displacement of the hydraulic motor
Note 1 to entry: The use of a variable displacement hydraulic motor permits the optimization of hydraulic
flow demand.
Note 2 to entry: The motor’s output torque, direction of rotation (if bi-directional) and associated operating
speed and resultant flow consumption is controlled by a servo valve which varies the motor’s displacement
which is typically operated in closed loop control.
Note 3 to entry: The specifications, design, manufacture and qualification of the servo valve is outside the scope
of this document.
3.1.1
uni-directional hydraulic motor
variable displacement hydraulic motor (3.1) that generates output torque via the drive shaft in only one
direction
3.1.2
bi-directional hydraulic motor
variable displacement hydraulic motor (3.1) that generates output torque via the drive shaft to both
clockwise and anti-clockwise directions
Note 1 to entry: Except for bi-directional over-centre hydraulic motors (3.1.3), bi-directional operation is typically
achieved by reversing the differential pressure across the inlet/outlet ports, thus reversing the output torque.
Note 2 to entry: Except for bi-directional over-centre hydraulic motors (3.1.3), the position of the swashplate is
controlled in each direction by a dedicated controller.
3.1.3
bi-directional over-centre hydraulic motor
bi-directional hydraulic motor (3.1.2) whose direction of rotation of the output drive shaft is controlled
by the angle of the motor swashplate which can go over centre
Note 1 to entry: This may be accomplished by controlling the position of the swashplate in each direction by a
single controller.
2 © ISO 2021 – All rights reserved

3.2
purchaser
organization that has the engineering responsibility for the system that includes the motor
Note 1 to entry: Typically, the purchaser is a system supplier (3.4), an aircraft manufacturer or a contractor.
3.3
detail specification
document compiled by the purchaser (3.2) that specifies the following:
a) technical requirements;
b) acceptance and qualification test requirements;
c) reliability, testability and maintainability requirements;
d) quality requirements;
e) packaging requirements;
f) other requirements
Note 1 to entry: Technical requirements include performance requirements and design requirements.
3.4
supplier
organization that provides the motor
Note 1 to entry: Typically, the supplier is the manufacturer of the motor who will be responsible for the design,
production, and qualification of the motor.
3.5.1
motor inlet port
port that receives flow from the hydraulic system to supply the motor
3.5.2
motor return port
port that returns flow back to the system reservoir
3.5.3
motor case drain port
port that drains internal leakage flow to the system reservoir
Note 1 to entry: Not all motors have a case drain port; instead the case drain fluid is supplied to the motor
outlet port.
3.5.4
shaft seal leakage port
port that routes any shaft seal leakage from the motor to an overboard drain, collector tank, ecology
bottle, etc.
3.6.1
rated temperature
maximum continuous temperature of the fluid to be supplied at the inlet port of the motor
3.6.2
normal operating temperature
temperature of the fluid to be supplied at the inlet port of the motor at which full performance of the
motor is required
3.6.3
minimum continuous temperature
minimum temperature of the fluid at the supply port of the motor at which the motor is able to function
Note 1 to entry: This temperature is generally higher than the minimum survival temperature (3.6.5).
3.6.4
extreme operating temperature
temperature of the fluid to be supplied at the inlet port of the motor at which the motor runs with an
agreed degraded performance
3.6.5
survival temperature
ambient temperature at which the motor is not required to run, but runs without degradation at the
normal operating temperature (3.6.2)
3.7.1
design operating pressure
normal maximum steady pressure
Note 1 to entry: Excluded are reasonable tolerances, transient pressure effects such as may arise from the
following:
— pressure ripple;
— reactions to system functioning;
— demands that may affect fatigue.
3.7.2
rated supply pressure
system rated pressure, which is normally the hydraulic power generation system design operating
pressure (3.7.1)
3.7.3
rated differential pressure
differential pressure measured between the motor inlet and outlet ports required to produce the rated
torque (3.11.1)
3.7.4
no-load break-out pressure
differential pressure required for starting the output shaft, without interruption, with the case drain
port at the rated case drain pressure (3.7.6.1) and the return port at the nominal motor return pressure
(3.7.5.1)
Note 1 to entry: This corresponds to break-out torque (3.11.2).
3.7.5.1
nominal motor return pressure
pressure generated at the return port as the motor returns flow back to the system
3.7.5.2
rated motor return pressure
maximum pressure at the return port
Note 1 to entry: This is applicable to uni-directional motors only.
Note 2 to entry: This is a stressing term only as the nominal motor return pressure (3.7.5.1) is generally
considerably less than the rated motor return pressure.
3.7.6.1
rated case drain pressure
nominal pressure at which the motor case is required to operate continuously in the system
4 © ISO 2021 – All rights reserved

3.7.6.2
maximum case pressure
maximum of either
— the maximum pressure peak that may be imposed by the hydraulic system on the motor case drain
port (3.5.3), or
— the pressure resulting from the internal bypassing of the rated flow towards the return and drain
ports in order to take into account the accidental transitory separation of the components
3.8
rated consumption
maximum flow rate measured at the motor inlet port (3.5.1) under the following conditions:
— rated fluid temperature;
— rated differential pressure (3.7.3);
— rated speed (3.10);
— using the hydraulic fluid specified in the detail specification (3.3)
3.9
maximum displacement
theoretical volume of fluid consumed by one revolution of the motor drive shaft at full stroke
Note 1 to entry: It is expressed in cubic centimetres per revolution (cubic inches per revolution).
Note 2 to entry: The maximum displacement is calculated from the geometrical configuration of the motor,
without allowing for the following effects:
— permissible manufacturing tolerances;
— distortions of the motor structure;
— the compressibility of the hydraulic fluid;
— internal leakage;
— temperature.
Note 3 to entry: The maximum displacement is used to indicate the size of the motor rather than its performance.
3.10
rated speed
maximum speed at which the motor is required to operate continuously at rated temperature (3.6.1)
and at rated differential pressure (3.7.3)
Note 1 to entry: The rated speed is expressed as the number of revolutions of the motor output shaft per minute.
3.11.1
rated torque
minimum torque value at rated operating conditions
3.11.2
break-out torque
minimum torque against which the motor will start at operating conditions specified in the detail
specification (3.3)
Note 1 to entry: This corresponds to no-load break-out pressure (3.7.4)
3.11.3
stalling torque
minimum opposing torque which stops the rotation of the outlet shaft at the rated supply pressure (3.7.2)
and for the outlet port and case drain port pressures specified in the detail specification (3.3)
3.11.4
maximum stalling torque
stalling torque (3.11.3) which can be generated at rated operating conditions
Note 1 to entry: This shall be specified to ensure that the motor’s torque capability in a stall (high efficiency)
condition does not overload the system’s capability (e.g. the shafts and gears, as applicable).
3.12
motor overall efficiency
e
value obtained from the formula
e = (o/i) × 100
where
o is the output shaft power (3.12.1);
i is the input fluid power (3.12.2)
Note 1 to entry: e is expressed in per cent.
Note 2 to entry: Calculating hydraulic power and mechanical power can be problematic unless the correct units
and associated equations are used:
— Metric units (torque – Nm; flow – L/min)
— Imperial units (torque – lb.in; flow – gpm)
3.12.1
output shaft power
o
value obtained from the formula
o = t × s
where
t is the shaft torque;
s is the shaft speed
3.12.2
input fluid power
i
value obtained from the formula
i = (p − r) × f
where
6 © ISO 2021 – All rights reserved

p is the inlet pressure;
r is the return pressure;
f is the rated flow
Note 1 to entry: This formula ignores compressibility effects. If this formula is to be used, the flow rate
measurement should be made on the compressed flow stream.
3.13
rated endurance
total number of hours and cycles of operation to be included in the endurance phase of its
qualification testing
3.14
first article inspection
FAI
process that conducts the following:
— verifies that the parts of a component comply with the drawings;
— verifies that the manufacturing processes have been compiled and are adhered to;
— verifies that the assembly processes have been compiled and are adhered to;
— verifies that the acceptance test of the component is in accordance with the test procedure, and that
the results of the test are in agreement with the test requirements
4 Classification
The hydraulic motors covered by this document are classified in two categories.
— Category A: Primary function motors, for example, flight controls, slats, flaps, adjustable planes,
power transfer units, constant speed drives, nosewheel steering.
NOTE ISO 22089 provides the variable displacement motor requirements for power transfer units.
— Category B: Secondary function motors, for example, hoists, guns, radars, doors.
In addition, the motor can be a uni-directional motor or a bi-directional motor.
The motor category and type (uni-directional or bi-directional or bi-directional over-centre) shall be
specified in the detail specification.
5 General requirements
5.1 Order of precedence
The detail specification shall take precedence in the case of a conflict between the requirements of this
document and the detail specification.
5.2 Hydraulic system characteristics
The hydraulic motor shall be designed to be operated by the hydraulic system as defined in the detail
specification.
The detail specification shall include the characteristics of the hydraulic system in which the motor
is to be used. This shall include the flow versus pressure curves for the supply, return, and case drain
lines for the following hydraulic fluid temperatures:
— normal operating temperature (e.g. +20 °C);
— rated temperature;
— minimum continuous temperature.
5.3 Airworthiness regulations
It is assumed that the hydraulic motor meets the applicable airworthiness requirements, whi
...