ISO 20574:2019

Road vehicles - Durability test method for starter motor for stop and start system

This document defines requirements and recommendations for starter motor durability testing of 12 V start systems for internal combustion engines. This includes test methods, test procedures and capabilities of test benches.

Véhicules routiers — Méthodes de test d'endurance pour les démarreurs stop and start system

General Information

• Status: Published
• Publication Date: 23-Apr-2019
• ICS: 43.060.50 - Electrical and electronic equipment. Control systems
• Technical Committee: ISO/TC 22/SC 32 - Electrical and electronic components and general system aspects
• Drafting Committee: ISO/TC 22/SC 32/WG 7 - Functional characteristics of starting devices and electrical generators
• Current Stage: 9060 - Close of review
• Completion Date: 02-Dec-2029

Overview

ISO 20574:2019 - Road vehicles - Durability test method for starter motor for stop and start system defines requirements and recommendations for durability testing of 12 V starter motors used in stop‑start systems for internal combustion engines. The standard specifies test methods, detailed test procedures, and the capabilities and minimum requirements for test benches so manufacturers and test laboratories can evaluate starter motor endurance under high‑cycle start conditions typical of stop‑start operation.

Key topics and technical requirements

• Test scope and planning
  • Defines test types using an actual engine or an engine simulator, and options to control tests via engine ECU or bench controller.
  • Requires a test planning matrix to set target cycle counts, sequences (manual, automatic, change‑of‑mind events), temperature targets and pass/stop criteria.
• Test bench capabilities
  • Minimum structural and measurement requirements, channel lists and control functionality for repeatable durability testing.
  • Annexes A–C describe test bench structures (Type 1–4) for different setups.
• Test procedures
  • Stepwise phases: installation/setup, pre‑check, test execution, post‑processing and reporting.
  • Emphasis on reproducible recording of starter motor voltage (U_STR), current (I_STR), cranking time, overrunning time and temperature.
• Supplemental methods
  • Brush temperature calibration, brush length measurement and starter motor input V–I curve verification to ensure thermal/mechanical stress is representative.
  • Measurement of pinion to ring gear axial gap and other mechanical checks relevant to wear.
• Reporting and acceptance
  • Documented reporting items and defined test stop criteria to determine pass/fail and enable consistent communication between suppliers and OEMs.

Practical applications and who uses it

• Starter motor manufacturers - for R&D, product validation and determining design margins for stop‑start duty cycles.
• Vehicle and engine manufacturers (OEMs) - to specify and verify supplier components and ensure system‑level durability under stop‑start usage.
• Independent test laboratories - to provide standardized, repeatable durability test reports for purchasing and engineering teams.
• Quality and supplier engineering - to set acceptance criteria, perform batch testing and support warranty investigations.

Related standards

• ISO 8856 (referenced normative standard) - electrical performance and test methods for starter motors; used alongside ISO 20574:2019 to cover electrical measurement and general requirements.

Keywords: ISO 20574:2019, starter motor durability test, stop‑start system, test bench, engine simulator, V–I curve, brush temperature, cranking, overrunning, starter motor manufacturer, vehicle manufacturer.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20574
First edition
2019-04
Road vehicles — Durability test
method for starter motor for stop and
start system
Véhicules routiers — Méthodes de test d'endurance pour les
démarreur stop and start system
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
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ISO copyright office
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Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
4 Planning of durability test . 4
4.1 Determination of durability test types . 4
4.2 Determination of durability test conditions . 4
4.3 Definition of cranking time, overrunning time . 7
5 Test bench equipment and information. 9
5.1 Test bench structure . 9
5.2 Minimum requirements of test bench . 9
5.3 Test bench measuring capabilities and channel list . 9
5.4 Test stop criteria .10
6 Detailed test procedures .11
6.1 Test procedure .11
6.1.1 General.11
6.1.2 Installation and setup stage for engine or engine simulator .11
6.1.3 Pre-check stage .12
6.1.4 Test execution stage .12
6.1.5 Post processing and reporting stage .13
7 Supplemental test methods .13
7.1 Brush temperature calibration .13
7.2 Starter motor input V-I curve and verification .15
7.3 Brush length measurement .16
7.4 Pinion to ring gear axial gap .17
Annex A (normative) Test bench structure (Type 1) .18
Annex B (normative) Test bench structure (Type 2) .19
Annex C (normative) Test bench structure (Type 3 and 4) .20
Annex D (informative) Summary of reporting items after the test .21
Foreword
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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
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Attention is drawn to the possibility that some of the elements of this document may be the subject of
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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 32,
Electrical and electronic components and general system aspects.
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.
iv © ISO 2019 – All rights reserved

Introduction
Stop and start systems contribute to fuel saving by stopping the engine when its operation is not
needed, and to start the engine automatically when its operation is needed. The more frequent starting
of the engine requires higher durability of the starter motor. Since there is no standard to evaluate the
durability of starter motors for stop and start systems, individual specifications are used by engine
and/or vehicle manufacturers and starter motor manufacturers. Because the stop and start systems
require much more frequent starter motor operations, the testing period is much longer compared to
conventional starter motors.
In addition to engine and/or vehicle manufacturers and starter motor manufacturers, testing companies
also began to conduct tests. In order to carry out the time-consuming test accurately and to use the test
results effectively, the test procedure in this document includes how to summarize the test results.
INTERNATIONAL STANDARD ISO 20574:2019(E)
Road vehicles — Durability test method for starter motor
for stop and start system
1 Scope
This document defines requirements and recommendations for starter motor durability testing of
12 V start systems for internal combustion engines. This includes test methods, test procedures and
capabilities of test benches.
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 8856, Road vehicles — Electrical performance of starter motors — Test methods and general
requirements
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms and definitions 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
stop and start system
system to stop the engine when its operation is not needed, and to start the engine automatically when
its operation is needed
3.2
manual start
event when the engine is started manually by the driver
3.3
automatic start
event when the engine is started by the stop and start system automatically
3.4
dummy starter motor
starter motor used for installation purpose only
3.5
calibration starter motor
starter motor used for calibration of test condition, which is equipped for measuring temperatures of
its components
3.6
engine simulator
device which simulates engine behaviour during engine start
3.7
battery simulator
electrical power supply equipment which simulates battery behaviour
3.8
engine mount
mechanical frame to support engine and gearbox
3.9
number of test start cycles
counted durability test start cycles
3.10
remaining brush length
length of brush after the test
3.11
usable brush length
length of brush that is available to be consumed
3.12
initial brush length
length of brush before starting the test
3.13
vehicle manufacturer
company which designs and produces vehicles
3.14
engine manufacturer
company which designs and produces internal combustion engines
3.15
starter motor manufacturer
company which designs and produces starter motors
3.16
cranking
condition in which the starter motor rotates the engine
3.17
overrunning
condition in which the engine rotates the starter motor pinion before starter motor OFF
3.18
engine ECU
electronic control unit for controlling internal combustion engine operation
3.19
starter solenoid
electromagnetic component of starter motor to move pinion and to switch electric motor
3.20
bi-control solenoid
starter solenoid which is able to control separately pinion movement and to switch electric motor
3.21
bench controller
device which is capable of controlling required test bench functions
2 © ISO 2019 – All rights reserved

3.22
nominal power
P
nom
power declared by the starter motor manufacturer corresponding to the maximum power output at the
reference temperature when determined according to ISO 8856
3.23
battery internal and line resistance
R
BL
sum of power supply (battery or battery simulator) internal resistance and total resistance of external
line (positive and negative sides and connections)
3.24
device under test
DUT
starter motor used for durability test
3.25
change of mind
CoM
start event before complete engine stall
3.26
starter motor voltage
U
STR
voltage at battery terminal of starter motor
3.27
starter motor current
I
STR
current drawn by starter motor
3.28
starter motor open circuit voltage
U
0_STR
voltage at starter motor terminals without electrical load
3.29
virtual starter motor voltage
U
0_STR_v
virtual starter motor voltage at I = 0A derived from V-I curve
STR
3.30
battery internal resistance
R
B
power supply (battery or battery simulator) resistance
3.31
line resistance
R
L
total resistance of external line (positive and negative sides and connections)
3.32
front end accessory drive
FEAD
equipment driven by belt which is connected to engine
3.33
starter motor temperature at control point
T
control
temperature measured at defined control point location
EXAMPLE At starter motor yoke surface.
3.34
temperature of starter motor brush
T
brush
temperature measured inside of starter motor brush
3.35
pinion to ring gear axial gap
d
prg
axial distance from front surface of pinion to ring gear at rest condition
3.36
starter motor input curve
V-I curve
straight line calculated from starter motor voltage vs starter motor current diagram defining starter
motor input conditions
4 Planning of durability test
4.1 Determination of durability test types
The durability test is performed with an engine simulator or an engine. The following test types can be
selected. See Table 1 for comparison of each test type.
1) Engine, using bench controller to control fuel/spark to specifically achieve pre-determined
cranking time and overrunning time (see Table 3).
2) Engine, using its engine ECU to control the test parameters.
3) Engine simulator, using engine waveform data provided by engine and/or vehicle manufacturers as
input to simulator (for cranking time, overrunning time, or torque) (see Table 3).
4) Engine simulator, using synthetic pattern or engine simulation model where starter motor
manufacturer or engine and/or vehicle manufacturers define values for torque, cranking and
overrunning behaviour (see Table 3).
Table 1 — Overview of test types
Test type Starter load Starter load characteristic Reference
1 Engine Engine using bench controller Annex A
2 Engine using engine ECU Annex B
3 Engine Simulator Engine simulation using engine waveform Annex C
data
4 Engine simulation using synthetic pattern Annex C
4.2 Determination of durability test conditions
The starter motor manufacturer and engine and/or vehicle manufacturers should define the test
conditions according to the test planning matrix shown in Table 2.
4 © ISO 2019 – All rights reserved

The following items should be specifically considered:
1) In case of engine simulator, multiple starter motors can be tested simultaneously with the same ring
gear. In that case, the orientation of the starter motors deviate from those of the target application.
Hence, the usage of multiple starter motors shall correspond to the test purpose (e.g. verification of
brush durability but not verification of pinion and ring gear durability).
2) The starter motor manufacturer and engine and/or vehicle manufacturers should agree starter
motor temperature level during the durability test. Different approaches to define temperature
level are established.
For example:
— test at maximum brush temperature defined by starter motor manufacturer;
— test at maximum brush temperature derived from vehicle real drive cycle; and
— test at an average brush temperature derived from brush temperature distributions of vehicle
real drive cycle.
Each approach covers different testing purposes such as focusing on thermal stress, test duration,
mechanical loads or balanced field representation.
3) The starter motor manufacturer and engine and/or vehicle manufacturers should define the test
pass criteria and define test stop criteria according to Table 6.
4) Additional test conditions may be defined and shall be documented in test planning matrix.
For example:
— always using “100 % new” battery for every test;
— testing with maximum pinion to ring gear axial gap; and
— number and orientation of starter motors mounted to engine simulator ring gear.
Table 2 — Test planning matrices
Test planning matrix (1/3) Reference
Test type (test type #1 to #4) 4.1
Target test duration (number of test start cycles)
Test sequence         x[M/S] +   x[A/S] +   x[CoM] +   x[A/S] +   x[CoM]
t                      s t                      s
1 2 Table 3
Manual start [M/S] t                      s t                      s
3 4
including
−1
NOTE 1
t                      s n                   min
5 1
t                      s t                      s Table 3 includ-
6 7
ing NOTE 2
Automatic start [A/S] t                      s t                      s
8 9
−1
t                     s n                   min
10 2
−1 −1
n                   min n                   min
3 4
CoM start [CoM] Table 3
t                     s
Table 2 (continued)
Engine information / Reference engine information for engine simulator
Engine manufacturer
Engine family or engine code
Engine ECU software version
Fuel type
Number of cylinders Displacement cm
FEAD components Exist /Not exist
FEAD belt tension N
Additional engine load Alternator operation Yes / No
Dual mass flywheel Exist / Not Exist
Others
°C < T
cool
Coolant temperature (T )
cool
Maximum        °C
Oil type
Engine coolant and oil
°C < T
oil
Oil temperature (T )
oil
Maximum         °C
Others
Number of teeth
Ring gear information Module
Others
Gearbox Type
Cranking waveform data (test
type 3) or synthetic pattern (test Specify the agreed data Table 3
type 4) in case of engine simulator
Test planning matrix (2/3) Reference
DUT information
Starter motor manufacturer
Starter motor family
Starter motor nominal power (P )                            kW ISO 8856
nom
Number of pinion teeth
Bi-control solenoid (Yes/No) 3.20
Others
Electric power supply (Battery or battery simulator)
Specify V-I graph or mathematical expres-
Starter motor input V-I curve
sion based on target vehicle or application 7.2
(U , R )
0_STR_v BL
measurement
Battery manufacturer, manufac-
tured date and size or battery
simulator type
Battery nominal voltage                                     V
Battery internal resistance (R )                               mΩ ( °C)
B
Line resistance (R )                             mΩ (  °C)
L
Tolerances for R , R , R and
B L BL
U
o_STR_v
Others
6 © ISO 2019 – All rights reserved

Table 2 (continued)
Others
Pinion to ring gear axial gap d                                     mm Figure 6
prg
Temperature at control point                  ±          °C
7.1
Location of control point
Agreed brush temperature limit
°C
7.1
Brush temperature measurement
position
Brush length initial check method 7.3
Starter motor input condition to
measure starter motor output per- Specify the agreed condition ISO 8856
formance
Starter performance after the test Agreed criteria ISO 8856
Test pass criteria 4.2
Test stop criteria 5.4
Reporting items Specify reporting items Annex D
Others
Test planning matrix (3/3) Reference
Data monitoring and recording : No / Yes, if yes define the data monitoring and record-

ing rate
Monitoring Recording
Battery voltage (optional) 5.3
Battery current (optional) 5.3
Starter motor voltage 5.3
Starter motor current 5.3
Starter motor input V-I curve 5.3

(U , R )
0_STR_v BL
Solenoid voltage 5.3
Solenoid current (optional) 5.3
Engine rotational frequency 5.3
Test start cycle count 5.3
Temperature at control point 5.3
Engine coolant temperature 5.3
Engine oil temperature 5.3
Others (specify) 5.3
4.3 Definition of cranking time, overrunning time
In the event that the engine ECU (or engine data) is not used in the setup (test types 1, 3 and 4, see
Table 1), it shall be necessary to decide and setup specific values for cranking time, or overrunning time
(see Table 3).
In that case, Table 2 should be used to help starter motor manufacturer and engine and/or vehicle
manufacturers to reach agreement on the necessary parameters as a part of the planning phase.
Table 3 — Parameters of each engine start
Manual start Automatic start Change of mind (CoM) start
t  time, in seconds
−1
n Engine rotational frequency, in min
t Cranking time of manual start
t Overrunning time of manual start
t Starter motor ON time of manual start
t Engine or engine simulator ON time of manual start
t Start cycle time of manual start (from start to restart)
t
...