Passenger cars -- Braking in a turn -- Open-loop test method

This document specifies an open-loop test procedure to examine the effect of braking on course holding and directional behaviour of a vehicle. Specifically, the method determines how the steady-state circular response of a vehicle is altered by a braking action only. This document is applicable to passenger cars as defined in ISO 3833 and to light trucks. The open-loop manoeuvre specified in this test method is not representative of real driving conditions but is useful to obtain measures of vehicle braking behaviour resulting from control inputs under closely controlled test conditions.

Voitures particulières -- Freinage en virage -- Méthode d'essai en boucle ouverte

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Status
Published
Publication Date
15-Apr-2019
Current Stage
6060 - International Standard published
Start Date
28-Mar-2019
Completion Date
16-Apr-2019
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INTERNATIONAL ISO
STANDARD 7975
Fourth edition
2019-04
Passenger cars — Braking in a turn —
Open-loop test method
Voitures particulières — Freinage en virage — Méthode d'essai en
boucle ouverte
Reference number
ISO 7975:2019(E)
ISO 2019
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ISO 7975:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© 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

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
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ISO 7975:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Variables ....................................................................................................................................................................................................................... 2

5.1 Reference system .................................................................................................................................................................................. 2

5.2 Variables to be measured ............................................................................................................................................................... 2

6 Measuring equipment ..................................................................................................................................................................................... 2

6.1 Description ................................................................................................................................................................................................. 2

6.2 Transducers and their installation ........................................................................................................................................ 3

6.3 Data processing ...................................................................................................................................................................................... 3

7 Test conditions ....................................................................................................................................................................................................... 3

8 Test methods ............................................................................................................................................................................................................. 3

8.1 Run-in program for newly installed brakes (pads/shoes) ................................................................................ 3

8.2 Warm-up....................................................................................................................................................................................................... 3

8.3 Brake temperature ............................................................................................................................................................................... 4

8.4 Initial driving condition .................................................................................................................................................................. 4

8.5 Performance of the braking procedure .............................................................................................................................. 4

8.6 General test description .................................................................................................................................................................. 5

9 Data evaluation and presentation of results ........................................................................................................................... 5

9.1 General ........................................................................................................................................................................................................... 5

9.2 Time histories .......................................................................................................................................................................................... 5

9.3 Braking action .......................................................................................................................................................................................... 5

9.3.1 Reference point in time, t ..................................................................................................................................... 5

9.3.2 Definition of times and requirements for standard evaluation ............................................... 6

9.3.3 Mean longitudinal acceleration, −a .......................................................................................................... 6

9.3.4 Mean longitudinal acceleration, −a , until time t ................................................................ 7

Xt,

9.4 Evaluation of characteristic values ........................................................................................................................................ 7

Annex A (normative) Presentation of results...........................................................................................................................................11

Bibliography .............................................................................................................................................................................................................................22

© ISO 2019 – All rights reserved iii
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ISO 7975:2019(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.

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 ISO/TC 22, Road vehicles, Subcommittee SC 33, Vehicle dynamics and

chassis components.

This fourth edition cancels and replaces the third edition (ISO 7975:2006), which has been technically

revised. The main changes compared to the previous edition are as follows:
— recognizing regenerative braking and active control systems.

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
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ISO 7975:2019(E)
Introduction

The main purpose of this document is to provide repeatable and discriminatory test results.

The dynamic behaviour of a road vehicle is a very important aspect of active vehicle safety. Any given

vehicle, together with its driver and the prevailing environment, constitutes a closed-loop system that

is unique. The task of evaluating the dynamic behaviour is therefore very difficult since the significant

interaction of these driver-vehicle-environment elements are each complex in themselves. A complete

and accurate description of the behaviour of the road vehicle will necessarily involve information

obtained from a number of different tests.

Since this test method quantifies only one small part of the complete vehicle handling characteristics,

the results of these tests can only be considered significant for a correspondingly small part of the

overall dynamic behaviour.

Moreover, insufficient knowledge is available concerning the relationship between overall vehicle

dynamic properties and accident avoidance. A substantial amount of work is necessary to acquire

sufficient and reliable data on the correlation between accident avoidance and vehicle dynamic

properties in general and the results of these tests in particular. If this test method is used for regulation

purposes, the correlation between test results and accident statistics should be checked.

© ISO 2019 – All rights reserved v
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INTERNATIONAL STANDARD ISO 7975:2019(E)
Passenger cars — Braking in a turn — Open-loop test
method
1 Scope

This document specifies an open-loop test procedure to examine the effect of braking on course holding

and directional behaviour of a vehicle. Specifically, the method determines how the steady-state circular

response of a vehicle is altered by a braking action only. This document is applicable to passenger cars

as defined in ISO 3833 and to light trucks.

The open-loop manoeuvre specified in this test method is not representative of real driving conditions

but is useful to obtain measures of vehicle braking behaviour resulting from control inputs under

closely controlled test conditions.
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 4138, Passenger cars — Steady-state circular driving behaviour — Open-loop test methods

ISO 15037-1:2019, Road vehicles — Vehicle dynamics test methods — Part 1: General conditions for

passenger cars
ISO 8855, Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8855 and ISO 15037-1 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
4 Principle

The purpose of this test is to examine the effect of braking on course holding and directional behaviour

of a vehicle. Specifically, the method determines how the steady-state circular response of a vehicle is

altered by braking action only.

The initial conditions are defined by constant longitudinal velocity and by a circle with a given radius,

as specified by the constant-radius test method of ISO 4138. The steering-wheel angle required for

the steady-state circular run shall be constantly maintained during the entire test. During the test,

the driver input and the vehicle response are measured and recorded. From the recorded signals,

characteristic values are calculated.
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ISO 7975:2019(E)
5 Variables
5.1 Reference system
The reference system specified in ISO 15037-1 shall apply.
5.2 Variables to be measured
The following variables shall be determined:
— moment of brake application (t );
— steering-wheel angle (δ );
— lateral acceleration (a );
— longitudinal acceleration (a );
— longitudinal velocity (v );
— yaw velocity (dψ/dt); and
— sideslip angle (β and/or lateral velocity (v ).

Strictly speaking, test results based on lateral acceleration should not be used for comparison of the

performance of different vehicles. This is because lateral acceleration is measured at right angles to

the intermediate X-axis and not perpendicular to the vehicle path. To overcome this difficulty, lateral

acceleration can be corrected for vehicle sideslip angle, which gives the centripetal acceleration.

However, the extent of this correction is not likely to exceed a few percent and may generally be

neglected.
It is recommended that the following variables be determined:

— pressure at master cylinder output or in the brake circuit which activates at least one of the front

wheel brakes p ); and
— wheel rotation speed (ωω− ).

The variables are defined in ISO 8855 except for stopping distance and the moment of brake application,

t , which is the instant at which the brake pedal is operated. The actuation of the brake pedal may be

determined by the use of a contact switch mounted directly on the brake pedal or a sensor for the brake

pedal force which set a trigger signal when the brake pedal force exceeds 10 N.
6 Measuring equipment
6.1 Description
ISO 15037-1:2019, Table 1 shall apply with the following additions from Table 1:
Table 1 — Variables, typical operating ranges and recommended maximum errors
Typical Recommended maximum error
Variable operating of the combined transducer/recorder
range system
Moment of brake application — 0,05 s
Pressure of braking system 30 MPa ±0,3 MPa
−1 −1 −1
Wheel rotation speed 0 s to 200 s ±2 s
a 6 2
1 MPa = 10 bar = 10 N/m .
2 © ISO 2019 – All rights reserved
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ISO 7975:2019(E)
6.2 Transducers and their installation
ISO 15037-1:2019, 5.2 shall apply.
6.3 Data processing

The recording system and data processing requirements contained in ISO 15037-1:2019, 5.3 shall apply.

7 Test conditions
The test conditions specified in ISO 15037-1:2019, Clause 6 shall apply.

General data on the test vehicle shall be recorded as specified in ISO 15037-1:2019, 6.4.1, with the

following additions:

The tyre type, tyre brand, any special equipment on the test vehicle, any deviation in type or operating

condition of components from the manufacturer’s specification, the odometer reading at the beginning

and end of the test, and any other condition that may affect test results shall also be recorded on the

test report for general data (see ISO 15037-1:2019, Annex A).
8 Test methods
8.1 Run-in program for newly installed brakes (pads/shoes)

The brake linings (pads/shoes) shall be conditioned following the recommendations of the vehicle

manufacturer. If manufacturer’s recommendations are not available, the brake linings shall be

conditioned using one of the following procedures:

For vehicles with disc/disc braking systems, a total of 60 brake applications shall be performed. From

an initial vehicle speed of 100 km/h, the vehicle shall be decelerated to approximately 20 km/h at the

following approximate deceleration rates:
— 2 m/s for the first 15 brake applications;
— 3 m/s for the next 15 brake applications; and
— 5 m/s for the final 30 brake applications.

For vehicles with disc/drum or drum/drum braking systems, a total of 200 brake applications shall be

performed. From an initial vehicle speed of 100 km/h, the vehicle shall be decelerated to approximately

20 km/h at the following approximate deceleration rates:
— 2 m/s for the first 50 brake applications;
— 3 m/s for the next 50 brake applications; and
— 5 m/s for the final 100 brake applications.

During these brake applications, brake disc and/or brake drum temperatures must not exceed

200 °C. The tyres used for running in the brakes must not be used for subsequent braking distance

measurements.
8.2 Warm-up

The procedure specified in ISO 15037-1:2019, 7.1 shall be followed to warm up the tyres and other

vehicle components prior to the test.

In addition to warming up the braking system, five full stops should be performed from an initial speed

of about 100 km/h. In each of these stops, brake actuation should be sufficient to cause the anti-lock

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ISO 7975:2019(E)

braking system to be active throughout the majority of the stop. To avoid excessive strain on the brakes,

the temperature of the brake discs (drums) should be below 120 °C at the beginning of each single stop.

8.3 Brake temperature

The temperature of the front brake discs (drums) shall be between 80 °C and 120 °C, and the rear brake

discs (drums) shall be less than 120 °C before each test run. If necessary, the brakes shall be cooled

between runs. The inst
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