GB/T 20948-2025Tractors for agriculture and forestry — Devices for indirect vision — Technical specification (English PDF)

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 of 6.7, each component shall be free from deformation, damage, or detachment, which may affect its function. The mirror direction shall be kept in the original normal operation position.

4.8 Moisture resistance

5.2 Position

5.2.1 The position of the exterior rear-view mirror shall be such that the

driver can clearly see the vision defined in 5.4 when sitting in the seat while driving normally.

5.2.2 The rear-view mirror shall be visible from the part of the windshield

wiper that is not operating, or from the side window of the tractor (if installed).

5.2.3 In the case of the maximum operation mass of the tractor, if the bottom edge of the rear-view mirror is less than 2m from the ground, the installation protrusion of the rear-view mirror shall be no more than 0.20m of the total width of the tractor.

5.3 Adjustment

5.3.1 The interior rear-view mirror shall enable the driver to make

adjustments at the driving position.

5.3.2 The exterior rear-view mirror shall enable the driver’s arm to make

adjustments by extending out of the tractor or outside the window.

5.4 Vision

5.4.1 Interior rear-view mirror (Class I)

The driver shall be able to see at least a vision area with a width of at least 20m on the horizontal road with the aid of the interior rear-view mirror. The center plane is the longitudinal reference plane of the tractor and extends from 60m behind the driver’s ocular points to the horizon, as shown in Figure 9.

5.4.2 Exterior rear-view mirror (Class II)

The driver shall be able to see a vision area with a left and right width of at least 4m on the horizontal road with the aid of the exterior rear-view mirror.

The left and right sides are parallel to the plane of the longitudinal reference plane of the tractor and are tangent to the left and right outermost points of the tractor, and extend from 20m behind the driver’s ocular points to the horizon. In addition, the driver shall be able to see a vision area with a width of 1m and connected with the above area from 4m behind the driver’s ocular points with the aid of the exterior rear-view mirror, as shown in Figure 10.

6.1 Measurement of the radius of curvature “C” of the protective frame

the sum of the regular reflectance and the diffuse reflectance.

6.4.1.3 Spectral characteristics of light sources and photodetectors

a) The light source consists of a CIE standard light source A and a lens that enables the light from the light source to be a parallel beam. In order to keep the light source voltage stable while the instrument is operating, a regulated power supply shall be used.

b) The spectral response of the photodetector carried by the receiving unit is proportional to the appropriate brightness function of the CIE (1931) standard colorimetric observer (SEE Appendix A). Other combinations of illuminator-filter-receiver that produce effects that are fully equivalent to CIE standard illuminator A and daylight vision may also be used. When an optical integrating sphere is used in the receiving unit, the inner surface of the sphere shall be coated with a matt (diffusely reflective), non-spectral selective, white paint.

6.4.1.4 Geometric conditions

a) The incident beam angle (theta) is preferably 0.44 rad ± 0.09 rad (25° ± 5°) from the perpendicular line perpendicular to the surface of the rear-view mirror, and shall not exceed the upper limit (0.53 rad or 30°). The angle (theta) of the receiver axis to the perpendicular line shall be equal to the incident beam angle (as shown in Figure 5). The diameter of the incident beam on the test surface shall be not less than 19mm. The area of the reflected beam covering the photodetector shall be less than the photosensitive area, but shall be no less than 50% of the photosensitive area, and as close as possible to the coverage area of the instrument during calibration.

b) When the optical integrating sphere is used for the receiving unit, the diameter of the sphere shall be no less than 127mm. On the sphere, the aperture of the incident beam of the rear-view mirror and the ball wall shall pass all of the incident beam and the reflected beam. The photodetector shall be placed in a position that is not exposed to incident and reflected beams.

6.4.1.5 Electrical characteristic of the photodetector, i.e., indicating

meter device On the indicating meter, the reading output by the photodetector is a linear function of the brightness on the photosensitive area. In order to facilitate zeroing and calibration, light, electricity or a combination of light and electricity may be used, but the method shall not affect the linearity and spectral characteristics of the instrument. The accuracy of the receiver, i.e., indicating system shall be within ±2% of full scale or within ±10% of the reading, whichever is less. a receiving unit Where:

E - Reflectance of the reference standard, %;

nE - Indication value of the reference standard reflectance on the indicating meter, %;

nX - Indication value of the rear-view mirror reflectance on the indicating meter, %;

X - Value calculated by the indirect method for the rear-view mirror reflectance, %.

6.5 Anti-impact test

6.5.1 Except as specified in 6.5.2, all rear-view mirrors shall be subjected to

the test specified in 6.5.

6.5.2 If the tractor is of maximum operation mass, all components on the

rear-view mirror are more than 2m above the ground (regardless of their adjustment position), the test specified in 6.5 may be exempt.

6.5.3 If the connectors (e.g., connecting plate, support frame, rotating shaft,

etc.) of the rear-view mirror does not exceed the projection width of the tractor and the height from the ground is less than 2m, the measurement shall be made on the vertical section of the bottom edge of the connectors of the rear-view mirror. If the rear-view mirror exceeds the width of the vehicle, the point on the cross section in the forward direction is taken as the standard. In this case, the rear-view mirror manufacturer or tractor manufacturer shall provide a description of the conditions in which the connectors are to be installed on the vehicle.

6.5.4 For rear-view mirrors that are not subjected to impact testing, the 2m

mark shall be marked on the support arm, and the results shall be indicated in the test report.

6.5.5 Impact test device

6.5.5.1 The impact test bench consists of a test-lens bracket and a

pendulum that may swing about two horizontal axes at right angles, one of which is in the plane of the vertical release trajectory. The end of the (mm);

d - Distance from the center of mass of the pendulum to the axis of rotation, in millimeters (mm).

6.5.6 Impact test method

6.5.6.1 The device for clamping the rear-view mirrors is provided by the

rear-view mirror manufacturer or the tractor manufacturer.

6.5.6.2 The positioning during the rear-view mirror test shall meet the

following requirements:

a) The rear-view mirror shall be fixed to the test bench according to the method recommended by the rear-view mirror manufacturer or the tractor manufacturer. The axis of its horizontal and vertical positions shall be the same as the actual state of operation.

b) If the rear-view mirror may be adjusted relative to its base, it shall be within the adjustment range specified by the rear-view mirror manufacturer or the tractor manufacturer, and at the most unfavorable position for rotation during impact.

c) If the rear-view mirror may be adjusted relative to its base, the regulating device shall be adjusted so that the holder is the closest to its base.

d) If the reflecting surface may be adjusted in the protective casing, the upper corner farthest from the tractor is adjusted to the maximum position of the protruding protective casing.

e) When the pendulum is in the vertical position, the horizontal plane and the vertical lead plane in the center of the sphere shall pass through the center of the mirror. The longitudinal swing direction of the pendulum shall be parallel to the longitudinal reference plane of the tractor.

f) When installing and adjusting according to the provisions of a) to d), if the parts of the rear-view mirror limit the return of the sphere, the impact point shall be adjusted perpendicular to the axis of rotation or the center of rotation, but it shall be determined that this adjustment is necessary to complete the test. One of the following requirements shall be met:

1) The outline of the sphere shall be at least tangential to the surface of the cylinder as described in 4.1.6;

2) The contact point of the sphere shall be at least 10mm from the edge of the reflecting surface.

6.5.6.3 During the test, the sphere is free to fall at an angle of 60° from the plumb line of the pendulum. When placed in the plumb position, the sphere strikes the rear-view mirror.

6.5.6.4 The rear-view mirror shall be subjected to impact under the following

different conditions:

7.2 The inspection of the rear-view mirror is divided into the exit-factory

inspection and the type inspection.

7.2.1 Exit-factory inspection

Rear-view mirrors shall comply with the provisions of 4.1.

7.2.2 Type inspection

7.2.2.1 In one of the following cases, the rear-view mirror manufacturer shall

perform a type inspection:

a) when new products are finalized;

b) when the product design, process and materials are greatly modified;

c) when the product is discontinued for one year and then resumed production, and when the production site changes or the production conditions change greatly;

d) products shall be batch- or mass-produced not less than once a year; and

e) when the national quality supervision and inspection agency puts forward the requirements for type inspection.

7.2.2.2 The rear-view mirrors for type inspection shall be taken immediately

from the same batch of products that have passed the exit-factory inspection.

No less than 10 samples of the same type and model shall be taken. First, the exit-factory inspection is re-checked. After the re-check is passed, the type inspection is carried out according to Table 5.

7.2.2.3 The type inspection of the rear-view mirrors shall comply with the

provisions of Table 5. If the items 2, 3, 4, 9, and 10 in Table 5 fail, the type inspection is judged to be unqualified. When other items fail, double-SAMPLE the rear-view mirrors to inspect the unqualified items. If there are still unqualified items, it is judged to be unqualified.

7.3 The sampling method is based on documents approved by the

prescribed procedures.

Table 5 -- Type inspection items Serial No. Item name Requirement Test No. 1 2 3 4 5 6 7 8 9 10 1 Appearance requirements 4.2 sqrt sqrt sqrt sqrt sqrt sqrt sqrt sqrt sqrt sqrt