About the Author
Liu Gong: with large state-owned enterprises and foreign enterprises
more than 20 years of work experience in the senior internal combustion
engine design engineers, good system to introduce the principles and
design experience.
Design of Engine Sliding Bearing
There are many bearings in the car engine, the most important of which is the rod bearing and crankshaft main bearing. After years of development, the engine with lubricated bearings in the structure has been basically stereotypes. Connecting
rod small head is pressed into the bushing, connecting rod bulk bearing
and shaft main bearing are generally divided into upper and lower half,
the embedded a bearing. Bearing wall thickness is generally not more than 3mm, by the "steel
back" cover friction alloy layer composition; also in the friction alloy
layer plus soft alloy coating composed of three thin-walled bearing.
At
present, the domestic bearing alloy raw material manufacturing process
is the use of centrifugal casting technology of Babbitt alloy bushings;
copper-based alloy bearing most of the centrifugal casting, some
manufacturers use copper-lead alloy powder sintering process billet; and
aluminum-based alloy bearings generally by the professional Manufacturers supply bimetallic strip. A
large number of foreign production of copper-based alloy pad are used
continuous casting method and continuous powder sintering method. The mechanical processing of the bearing pad is carried out in the
professional bearing factory, and towards the mechanization, automation,
continuous production mode of development.
1
General steps for engine plain bearing design
(1) combined with the overall design, to determine the bearing structure type and the main size.
(2) combined with the power calculation, determine the bearing load, draw the load map.
(3) check the bearing pressure and linear velocity, determine the bearing alloy material.
(4) for hydrodynamic performance calculation, drawing the axis of the
track and oil film pressure distribution map; select the lubricating
oil; determine the bearing clearance, lubricating oil inlet temperature,
pressure and other relevant parameters of the reasonable value.
(5) for the bearing, sleeve and other parts of the structural design, drawing work map.
2
Bearing design to consider the main issues
(1)
Select the appropriate bearing friction-reducing alloy material and
surface coating, so that it has sufficient anti-fatigue strength, to
resist the oil film pressure caused by the pulse load, to ensure that
the bearing in normal use without damage, abrasions and Too fast wear.
(2) choose a reasonable bearing width ratio, oil tank, bearing
clearance and inlet position, etc., to create a hydrodynamic
lubrication.
(3) choose a reasonable degree of transparency and free play. To ensure that the bearing will not rotate in the hole and can come out of friction heat.
(4)
to ensure that the steel back of the thin-walled bearing has a high
compression yield limit, the bearing in the circumferential direction of
the uniformity of the bearing bolts layout and design to maintain the
joint surface in all conditions sufficient preload pressure. Although there are many empirical data, data and some theoretical
calculations can be designed at the time of reference, but some factors
are difficult to set, and some factors are not included in the
theoretical analysis, so the evaluation of bearing design can only be
engine test.
(5)
with three-layer bearing can significantly improve the anti-corrosion,
anti-bite, vibration-resistant ability, and thus the highest fatigue
strength. Surface
coating appropriate selection, the initial overheating caused by the
alloy surface flow, adhesion from the "ironing" role. The strain of the alloy layer has the effect of damping vibration.
(6) thin-walled bearing should be fully tightened, so that tile back
in the bottom hole in order to improve the cooling effect and improve
the stress distribution.
(7) in the structural design to change the unsuitable oil tank, oil hole location and size.
Engine sliding bearing material
1
The main requirements of the engine for sliding bearing materials
From the engine bearing the working conditions to consider the
requirements of the bearing material is multifaceted, which mainly have
the following few.
(1) have a high enough fatigue strength. The load acting on the bearing has an alternating and impact. The
bearing friction-reducing alloy material should have the same fatigue
strength as the load, so as to avoid cracking and peeling. It is
required to have the bonding strength between the steel back and the
alloy layer and have sufficient bonding strength. The mechanical properties (strength and hardness) of the bearing alloy
should also vary with temperature to accommodate the bearing's
performance requirements at high temperatures.
In
addition, the bearing capacity of bearing alloy and the bearing and
bearing stiffness are related to the smaller deformation, alloy layer
stress is smaller, the higher the carrying capacity. The bearing has a steel back and the thickness of the
friction-reducing alloy layer is small (no more than 0.4 mm) for the
reason.
(2) have good anti-friction properties, including anti-bite Taiwan, nestability and compliance. Anti-bite
is the temporary interruption of the oil film, bearing and journal
surface with local direct contact, high friction temperature (start and
stop process, suddenly off the oil, etc.), bearings and journals are not
easy to bite each other and abrasions Nature, which is related to the lipophilicity of the bearing alloy. Lipophilic
good, to maintain the ability of the border oil film, oil film cut off
after the recovery is also fast, then the bearing resistance to seizure
like. Inclusion
means that the bearing alloy allows a small amount of hard dust, debris
and other fine particles embedded in the alloy layer and avoid
scratching the indica and consequently the ability to hurt themselves. Compliance refers to the ability of the bearing alloy layer to
accommodate journal geometry deviation or deformation to reduce edge
loading and wear, uniforming load and wear.
Bearing
resistance to the occlusal, embedded and good adaptability, bearing
alloy and matching journal is more wear-resistant, long life: but the
bearing wear resistance and other factors, such as bearing hardness,
journal material, Hardness, surface roughness and lubrication
(3) Corrosion resistance. In the use of crankcase oil constantly oxidized deterioration, the
formation of organic acids and peroxy compounds, the bearing surface
corrosion, so the bearing alloy has a good corrosion resistance.
(4) anti-corrosive. Bear the bearing surface lubrication of the local pressure drop caused by the ability of bubble burst damage.
(5) The tile material should have sufficient compression yield limit. The
tile material must be of sufficient strength to bond directly or
through the intermediate layer and the friction-reducing alloy layer. On
the other hand, the bearing pad must be fitted in the bearing housing
hole with sufficient interference, and the tile material must have a
sufficiently high yield limit. Low
carbon steel is in line with the above requirements of the material,
commonly used in China 08,10 and 15 high-quality carbon steel. Almost no bearing friction reduction alloy can meet the above requirements at the same time. In
general, the harder material has a higher mechanical properties, the
softer material has a better surface friction performance. The
reason why widely used in the basic alloy layer plus soft alloy coating
(thickness 0.013-0.03 dish) three-tier pad structure, is to improve the
surface friction performance while maintaining the basic alloy layer of
higher machinery performance.
2
Bearing friction reduction alloy material
Engine bearing alloy material variety, can be divided into babbitt,
copper-based alloy and aluminum-based alloy three categories.
2.1 Babbitt
Pasteur is divided into tin and lead. In the soft pick matrix or lead matrix are distributed with hard spots (SnSb,
Cu6Sn6, antimony solid solution, etc.). The soft matrix determines that the babbitt has good lipophilicity, resistance to seizure, compliance and embedding
Possession of the oil filter requirements are relatively low. Soft cloth in the uniform distribution of the rodent paste has a good wear resistance. The biggest drawback of Babbit is the low fatigue strength.
2.2 copper-based alloy
Steel-based alloys with tough copper as the matrix. According to the second major component of the alloy is divided into lead bronze, tin bronze and aluminum bronze. These
bearing materials have the advantages of fatigue strength, large
carrying capacity, and the mechanical properties vary with temperature,
so the allowable pressure and allowable working temperature are greater
than the babbitt and aluminum alloy. Disadvantages
are poor adaptability and hiding, the parts processing, processing
accuracy and oil filtration quality requirements, and requires a higher
hardness of the journal. In addition, the lead in the alloy is susceptible to acid corrosion, requiring corrosion in the oil additives. In
order to improve the friction and corrosion resistance of the bearing
surface, a layer of soft alloy is electroplated on the alloy layer,
which provides the flexibility to ensure the effective operation of the
crankshaft system. The current bearing of this material is mainly used
High-strength supercharged diesel engine.
Tin bronze and aluminum bronze allowable than the pressure and wear
resistance is higher than the lead bronze, mainly used for connecting
rods small head bushings.
2.3 Al-based alloys
With aluminum as the basic ingredient. And
its second component is divided into aluminum-tin alloy,
aluminum-silicon alloy and aluminum-lead alloy, aluminum integrated gold
pad with good overall performance, its anti-occlusal, embedded,
compliance, corrosion resistance, process and economy Are better than copper-lead alloy bearing, fatigue strength and load capacity is better than Babbit. Therefore, aluminum-based alloy bearing can be said to be the first
one of the bearing material (about 75%), of which the most widely used
aluminum-tin alloy.
Bearing alloy composition and comprehensive performance in Table 1 and Table 2.
Table 1 common alloy friction alloy basic chemical composition
The following are the same as the "
Table 2 Commonly used bearings and bushing alloy materials, the overall performance and use
The following are the same as the "
Table 3 Chemical composition of surface coating
Table 4 The relationship between the thickness of the coating and the fatigue strength
The following are the same as the "
2.4 Surface coating material
Electroplating
in the copper-lead alloy, low-tin aluminum alloy and aluminum-silicon
alloy pad surface of the soft alloy material, commonly used in Table 3. The
main role of the coating is to improve the corrosion resistance of the
bearing, anti-bite, compliance and embedded, but also improve the
bearing fatigue strength and carrying capacity. To meet the high-speed high-load engine performance requirements of the bearing. Coating thickness 0.013-0.03mm, its thickness will increase the fatigue strength, bearing alloy layer is easy to peel off. The relationship between the thickness of the coating and the fatigue strength is shown in Table 4.
2.5 connecting rod small head bushing material
Generally
use the full floating piston pin connecting rods are small holes in the
hole with a wear-resistant with wear-resistant bushing. Commonly used material is CuPbl0Snl0. Also useful QSn4-4-2.5 tin green steel material (such as CA6102 gasoline engine connecting rod small head bushing material).
Design of small head bushing reference standard GBl2613 (sliding bearing roll sleeve)
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