ISO 7902-3:2020

INTERNATIONAL ISO
STANDARD 7902-3
Second edition
2020-06
Hydrodynamic plain journal bearings
under steady-state conditions —
Circular cylindrical bearings —
Part 3:
Permissible operational parameters
Paliers lisses hydrodynamiques radiaux fonctionnant en régime
stabilisé — Paliers circulaires cylindriques —
Partie 3: Paramètres opérationnels admissibles
Reference number
ISO 7902-3:2020(E)
©
ISO 2020

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ISO 7902-3:2020(E)

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ISO 7902-3:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 1
5 Operational parameters to avoid wear . 2
5.1 Minimum permissible lubrication film thickness . 2
5.2 Effective waviness and maximum permissible effective waviness . 2
6 Operational parameters to avoid excessive mechanical loading . 6
7 Operational parameters to avoid excessive thermal loading . 7
8 Operational parameters for the bearing clearance . 8
Bibliography . 9
© ISO 2020 – All rights reserved iii

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ISO 7902-3:2020(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
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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
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 8,
Calculation methods for plain bearings and their applications.
This second edition cancels and replaces the first edition (ISO 7902-3:1998), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— adjustment to ISO/IEC Directives, Part 2:2018;
— correction of typographical errors.
A list of all parts in the ISO 7902 series can be found on the ISO website.
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.
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ISO 7902-3:2020(E)

Introduction
In order to attain sufficient operational reliability of circular cylindrical plain journal bearings when
calculated in accordance with ISO 7902-1, it is essential that the calculated operational parameters
h , T or T and p do not lie above or below the permissible operational parameters h , T and
min B ex lim lim
p . The permissible parameters represent geometrically and technologically dependent operational
lim
limits within the plain bearing tribological system. They are empirical values which still enable
sufficient operational reliability even for minor influences (see ISO 7902-1).
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INTERNATIONAL STANDARD ISO 7902-3:2020(E)
Hydrodynamic plain journal bearings under steady-state
conditions — Circular cylindrical bearings —
Part 3:
Permissible operational parameters
1 Scope
This document specifies empirical permissible values for h , T and p .
lim lim
lim
The empirical values stated can be modified for certain applications, for example if information supplied
by the manufacturer is to be taken into account. The descriptions of the symbols and calculation
examples are given in ISO 7902-1.
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 7902-1, Hydrodynamic plain journal bearings under steady-state conditions Circular cylindrical
bearings — Part 1: Calculation procedure
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Symbols and units
Symbols and units are defined in Table 1. ISO 7902-1:2020, Table 1 shall be referenced to identify the
meaning of symbols not listed in Table 1.
Table 1 — Symbols and their designations
B Nominal bearing width m
C Nominal bearing clearance m
D Nominal bearing diameter (inside diameter) m
E Dimensionless modulus of elasticity 1
G Dimensionless shear modulus 1
h Waviness of sliding surface (from Figure 3) m
wav
h Effective waviness of sliding surface m
wav,eff
h Maximum permissible effective waviness m
wav,eff,lim
h Maximum permissible waviness m
wav,lim
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ISO 7902-3:2020(E)

Table 1 (continued)
i Number of waviness 1
l Length of lubrication groove m
G
l Length of lubricant pocket m
P
L Length of bearing housing m
H
−1
N Rotational frequency of the bearing force s
F
3
Q Lubricant flow rate at the inlet to clearance gap m /s
1
3
Q Lubricant flow rate at the outlet to clearance gap m /s
2
Rz Average peak-to-valley height of bearing sliding surface m
B
Rz Average peak-to-valley height of shaft mating surface m
J
y Amount of deflection m
γ Angle of misalignment of the shaft rad
Period of waviness °
ϕ
wav
5 Operational parameters to avoid wear
5.1 Minimum permissible lubrication film thickness
The aim of keeping above the minimum permissible lubrication film thickness h is to retain complete
lim
lubrication of the plain bearing in order to attain least possible wear and low susceptibility to faults.
The lubricant should be free of contaminating particles, otherwise increased wear, scoring and local
overheating can result, thus impairing correct functioning of the plain bearing. If necessary, appropriate
filtering of the lubricant should be provided for.
The minimum permissible lubrication film thickness h , as a characteristic parameter for the
lim
transition to mixed friction (see ISO 7902-1:2020, 7.6), can be determined from the following formula as
shown in Figure 1.
1 1
hR=+zRzB+⋅yy++h (1)
limB Jwav,eff
2 2
Formula (1) takes into account
— the sum of the mean peak-to-valley heights of bearing and shaft at the ideal location (line X-X)
[Rz + Rz ],
B J
— the mi
...