GB/T 37677-2019 PDF English
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Plain bearings - Recommendations for automotive crankshaft bearing environments
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GB/T 37677-2019: PDF in English (GBT 37677-2019) GB/T 37677-2019
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 21.100.10
J 12
Plain bearings - Recommendations for automotive
crankshaft bearing environments
(ISO/TR 27507:2010, MOD)
ISSUED ON: JUNE 04, 2019
IMPLEMENTED ON: JANUARY 01, 2020
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of PRC;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
Introduction ... 4
1 Scope ... 6
2 Crankshaft ... 6
3 Bearing seat ... 11
4 Conclusion ... 14
Appendix A (Informative) Technical differences between this standard and
ISO/TR 27507:2010 and their causes ... 15
Plain bearings - Recommendations for automotive
crankshaft bearing environments
1 Scope
This standard gives the recommended parameters for the working environment
of automotive engine crankshaft bearings. It is explained that in order to meet
the working environment of crankshaft bearings, with the current processing
equipment, the various sizes and states related to the crankshaft bearing
environment that most engine manufacturers can achieve, such environment
for crankshaft bearing will not cause bearing problems.
Some of the recommended parameters in this standard cannot be fully met for
certain applications. In these applications, design specifications require more
precise high-quality parts.
2 Crankshaft
2.1 Surface roughness
The rougher the journal surface, the more likely it is that the rough surface
contact will have a destructive effect on the lubricant film and the higher the
wear rate. Excessive surface roughness will reduce the thickness of the
lubricant film to the extent that overheating or even seizure occurs.
Generally, the surface roughness of the crank pin and the main journal shall not
be greater than Ra0.25 μm. The roughness of the thrust surface shall never be
greater than Ra0.4 μm. Experience and tests have shown that the load that the
thrust ring can withstand is inversely proportional to the roughness of the
matching surface. Therefore, it is necessary to finish the thrust surface to a
state much lower than Ra0.4 μm.
2.2 Grinding and polishing
When grinding standard cast iron shafts, nodular graphite will be exposed and
fall off from the surface of the material, thus forming fiber filaments or tongue
thorns in these shed pits of the iron substrate. During operation, these fiber
filaments can become embedded in the bearing alloy and can quickly cause
severe wear and damage. Therefore, it is common practice to polish the
crankshaft after grinding to remove these raised tongue thorns. The direction of
these tongue thorns on the shaft surface depends on the direction of rotation
3 Bearing seat
3.1 Overview
The shape of automotive thin-walled bearings mainly depends on the contour
shape of the bearing seat hole, then affects the shape of the bearing hole, so
the machining of the bearing seat hole is very important.
3.2 Surface roughness of seat hole
The close contact between the bearing and the seat hole is very important for
the good heat transfer and heat dissipation of the bearing; and to prevent
displacement and fretting wear in the interference state. The surface roughness
of the connecting rod seat hole shall not exceed Ra0.8 μm; the surface
roughness of the crankshaft bearing seat hole shall not exceed Ra1.6 μm; the
surface roughness shall be avoided from exceeding these recommendations,
because the roughness exceeding the limit will reduce the heat conduction of
the bearing back to the seat, thereby causing overheating in the bearing
clearance.
3.3 Tolerance of seat hole size
For main bearing seat holes, the diameter tolerance is usually specified as 25
μm; for connecting rod holes below 80 mm. The diameter tolerance shall be
controlled at 12.5 μm if possible, especially under heavy loads. For automotive
bearing, it is usually desirable to be 20 μm ~ 25 μm. Very large connecting rods
with a diameter tolerance of 25 μm are acceptable. If the bearing clearance
needs to be strictly controlled, tighter tolerances on the seat holes are required.
3.4 Cylindricality of seat holes
See Table 3 for the cylindricality deviation limits for the large end hole of the
connecting rod and the main bearing block. If the deviation from the cylindrical
geometry is too large, a concentrated load will be formed on the bearing,
resulting in high lubricating film pressure and low oil film thickness at the
corresponding location. Cylindricality is the most critical at heavy loads. For
heavy-duty short bearings, the smaller the cylindricality in the load area, the
better.
Because not only the taper, but also the shape errors such as hourglass and
drum shape affect the cylindricality, in order to accurately evaluate and
effectively control the cylindricality, each journal shall be subject to diameter
measurement in three cross-sections such as the both axial ends and middle
part.
3.7 Parallelism of connecting rod holes
The parallelism and twist between the large-end hole and the small-end hole of
the connecting rod are measured at the 150 mm length of connecting rod, which
shall be controlled at 25 μm.
3.8 Alignment of oil hole
The oil hole on the bearing must be aligned with the oil hole on the seat hole;
the deviation is not more than 750 μm.
3.9 Fitting of the positioning lip
The function of the positioning lip of the thin-walled bearing is to prevent the oil
holes from being blocked by each other. Therefore, it is required that the
distance from the bearing seat to the end surface of seat hole and from the
positioning lip groove on the bearing cover to the end surface of the seat hole
are different; secondly, the upper and lower bearings and the seat hole do not
have a significant axial displacement. Therefore, the coordination of the
positioning lip and the positioning groove shall be clearance fit in the three
directions of length, width and height, so as to prevent mutual interference from
causing the poor fit of the bearing back around the positioning lip, raising the
surface of local bearing, thereby causing damage. See Table 4 for minimum
fitting clearance.
Table 4 -- Fitting clearance of positioning lip and groove
Diameter of seat hole DH / mm Minimum fit clearance / mm
> ≤ Width Height Length
- 50
0.14
0.4 0.5
50 80 0.45 1.0
80 120 0.50 1.5
3.10 Positioning of bearing seat cover
The bearing seat is generally positioned by bolts, fractures, steps, toothed joint
surfaces or positioning pins on the joint surface of the bearing seat by twisted
holes. However, the tooth-shaped joint surface method is not recommended,
because it is impossible to completely contact between the two surfaces. The
positioning of the bearing cover, especially the radial positioning, is very
important, because the slightest misalignment will also cause a step at the
bearing joint surface, which will generate uneven loads and may even damage
the lubricant film.
The positioning of the bearing cover must be reliable, and even the positioning
surface must have a slight interference fit. In the case of bolt fastening, with the
change of bolt torque, even if it is very well positioned, a certain misalignment
may occur. The step caused by the misalignment shall not exceed 12.5 μm.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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