GB/T 20948-2007 English PDF (GBT20948-2007)

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GB/T 20948-2007: Rear-view mirrors requirements for agricultural and forestry tractors
GB/T 20948-2007
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 65.060.10
T 68
Rear-view mirrors requirements for
agricultural and forestry tractors
ISSUED ON: JUNE 25, 2007
IMPLEMENTED ON: NOVEMBER 1, 2007
Issued by: General Administration of Quality Supervision, Inspection
and Quarantine of the People’s Republic of China;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative references ... 4 
3 Terms ... 4 
4 Performance requirements ... 7 
5 Installation requirements ... 11 
6 Measurement and devices and test methods ... 12 
7 Inspection rules ... 24 
8 Marking, packaging, transportation and storage ... 26 
Appendix A (Normative) Spectral tristimulus values of the CIE standard
colorimetric observer ... 28 
Rear-view mirrors requirements for
agricultural and forestry tractors
1 Scope
This Standard specifies the definitions, performance requirements,
installation requirements, test methods, inspection rules and marking,
packaging, transportation and storage of rear-view mirrors for agricultural and
forestry wheeled and crawler tractors.
This Standard applies to the agricultural and forestry wheeled and crawler
tractors.
2 Normative references
The provisions in the following documents become the provisions of this
Standard through reference in this Standard. For dated references, the
subsequent amendments (excluding corrections) or revisions do not apply to
this Standard. However, parties who reach an agreement based on this
Standard are encouraged to study if the latest editions of these documents
are applicable. For undated references, the latest editions apply to this
Standard.
QC/T 625-1999 Metallic coatings and conversion coatings for automobile
QC/T 484-1999 Automobile paint coatings
ISO 5353:1995 Earth-moving machinery, and tractors and machinery for
agriculture and forestry - Seat index point
3 Terms
The following terms and definitions are applicable to this Standard.
3.1 Rear-view mirror
A device that is able to see the rear and side images of the tractor within the
vision specified in 3.10.
3.2 Interior rear-view mirror
A device that meets the vision defined in 3.1 and is mounted in the tractor
cab.
3.3 Exterior rear-view mirror
A device that meets the vision defined in 3.1 and is mounted on the outer
surface of the tractor.
3.4 Class of rear-view mirror
Various rear-view mirrors with one or more common features or functions.
Class I is an interior rear-view mirror; and Class II is an exterior rear-view
mirror.
3.5 Center of the mirror
The center of mass of the visible area on the reflecting surface.
3.6 Principal radius of curvature at one point obtained on the
reflecting surface (ri, ri’)
The radius of curvature measured by the instrument specified in 6.3.1 through
the center of the reflecting surface, parallel to the line segment b of the mirror
and perpendicular to the direction of the line. See 4.3.1.2 for the
determination of line segment b.
3.7 Radius of curvature at one point on the reflecting surface (rpi)
Refer to the arithmetic mean value of the principal radius of curvature:
Where:
rpi - Radius of curvature at the ith point, in millimeters (mm);
ri, ri’ - Principal radius of curvature measured in two mutually perpendicular
directions at the ith point, in millimeters (mm).
3.8 Radius of curvature of the constituent parts of the rear-view mirror
(C)
C refers to the radius of the arc of the curved shape of the components such
as protective frame, support frame, and connecting member of the rear-view
mirror.
3.9 Driver’s ocular points
4.1.5 For the edge of the fixed hole or recess with a diameter or a maximum
diagonal of less than 12mm on the rear-view mirror, if it has been rounded,
the requirements for radius of curvature in 4.1.4 are not necessarily met.
4.1.6 The connection of the rear-view mirror to the tractor is designed to
ensure that the rear-view mirror is offset from the axis of rotation or the center
of rotation in the direction of impact, or either of them, to form a cylinder with a
radius of 50mm. The cylinder shall be cut at least to the surface portion to
which the connector is attached.
4.1.7 For exterior rear-view mirrors, if the parts involved in 4.1.3, 4.1.4, and
4.1.5 are made of materials not greater than Shore hardness of A60, it is not
necessary to meet the above requirements.
4.1.8 For interior rear-view mirrors, if the parts on the rear-view mirrors are
made of materials less than Shore hardness of A50 and mounted on a steel
support, the tests of 4.1.3 and 4.1.4 apply only to this support.
4.2 Appearance requirements
4.2.1 Under the illumination condition of 500 lx, when the mirror surface is
viewed from the 45° direction at 500mm from the naked eye, there shall be no
defects such as deformation, blur, streaks, bubbles, scratches, cracks and
inclusions on the rear-view mirror surface.
4.2.2 Rubber parts shall not have obvious defects such as damages and
cracks.
4.2.3 Plastic parts shall not have obvious defects such as fading, cracks,
scratches and deformation.
4.3 Performance requirements
4.3.1 Size requirements
4.3.1.1 Interior rear-view mirror (Class I)
It shall be possible to draw a rectangle with a base of a and a height of 40mm
on the reflecting surface. The size a is calculated according to the Formula
(2).
Where:
4.4.3.2 The difference between rpi (rp1, rp2 and rp3) value and r value of the
radius of curvature at any point shall be no more than 0.15r.
4.5 Reflectance
4.5.1 The reflectance value determined according to the method specified in
6.4 shall be not less than 40%. If the rear-view mirror has two working
positions (daytime and nighttime), the color signal of road traffic shall be
correctly recognized when it is in the daytime position, and the reflectance
value at nighttime position shall be no less than 4%.
4.5.2 Except for long-term rear-view mirrors under extremely harsh weather
conditions, the reflectance shall meet the reflectance values specified in 4.5.1
during normal use.
4.6 Impact resistance and bending resistance
4.6.1 The rear-view mirrors shall be subjected to an anti-impact test in
accordance with 6.5 and subjected to an anti-bending test in accordance with
6.6.
4.6.2 When the rear-view mirror performs the anti-impact test specified in
6.5 and the anti-bending test specified in 6.6, the reflecting surface shall not
be broken, but the following two conditions may be considered as meeting the
requirements:
4.6.2.1 The shards of glass remain attached to the protective casing or to
objects that are firmly attached to the protective casing. The glass is allowed
to partially detach from the above portion, but the length of any side of the
rupture shall not exceed 2.5mm. At the point of impact, small shards are
allowed to detach from the above portion.
4.6.2.2 The reflecting surface is made of safety glass.
4.6.3 For the rear-view mirror attached to the windshield glass, if the
support member of the rear-view mirror is damaged during the impact test,
the residual part of the protruding base shall be no more than 10mm, and the
shape shall still meet the requirements of 4.1.4 and 4.6.2.
4.7 Vibration resistance
When the vibration resistance of the rear-view mirror is tested in accordance
with the provisions o...