Characteristics and Selection of Sliding Bearings for Vehicles
Abstract: In order to improve the quality of diesel engine repair and ensure the selection and repair of sliding bearings, this article provides a detailed explanation of the performance and characteristics of bearings, and highlights the precautions to be taken when repairing sliding bearings in modern automotive engines.
【 Keywords 】: sliding bearings; Diesel engine; Repair quality
1. Performance and characteristics of sliding bearings
In the selection and repair of sliding bearings, it is necessary to have a comprehensive understanding of the performance and characteristics of the bearings. Because bearings made of different materials are suitable for different engines, such as copper lead alloy and high tin aluminum alloy bearings with hard matrix and soft particles are suitable for high-power, high-speed heavy-duty diesel engines, while white alloy bearings with soft matrix and hard points are mostly used for small and medium-sized engines. The clearance between bearings and shaft necks of different materials varies.
(1) Tin based Babbitt alloy bearings: Tin based Babbitt alloy is an early used anti-wear alloy material in engine bearings. This alloy is a soft matrix hard point material with good wear resistance, embeddedness, and compliance. Its major drawback is low fatigue strength. Especially when the temperature exceeds 100 ℃, its hardness and strength sharply decrease.
(2) High tin aluminum alloy bearings: The main component of this alloy is aluminum, with tin accounting for 20%, so it is also known as 20 tin aluminum alloy. Its organization is uniformly distributed with soft particles on a hard substrate, so it has high load-bearing capacity, allows for high linear velocity, and has good anti adhesion and anti bite performance, thus meeting the requirements of high-speed diesel engines.
(3) Copper lead alloy bearings: Copper lead alloy is a hard substrate of copper with uniformly distributed soft lead particles that do not melt in copper. Its outstanding advantages are high load-bearing capacity, good fatigue resistance, and mechanical properties are not greatly affected by temperature changes. Even at 250 ℃, it can still work normally. However, copper lead alloy bearings have the following disadvantages compared to white alloy bearings: a. Poor compliance and embedment. b. Easily susceptible to acidic corrosion, requiring high quality of lubricating oil. c. The mutual melting degree of copper and lead is very low, and they can hardly melt at room temperature, resulting in segregation phenomenon. d. Poor sensitivity to faults. When the engine burns due to lack of oil or improper repair during operation (resulting in varying degrees of adhesive biting), the high melting point and hardness of copper can cause the surface of the shaft neck to heat up violently, leading to roughening, bluing, annealing, or cracking. And the white alloy has already softened before melting, and the journal can automatically iron out the bite, so not only will the journal not be damaged, but the bearing can also continue to work without obvious damage. Even if a complete adhesive bite occurs, the white alloy will adhere to the surface of the journal, thereby protecting the journal from damage. Practice has shown that after the occurrence of tile burning and shaft holding accidents in white alloy bearings, there is no obvious strain on the shaft neck, the hardness will not decrease, and no quenching cracks will occur.
(4) Three layer metal bearings: Generally, bearings are composed of two layers of metal: steel backing and bearing alloy. In order to improve the surface performance of copper lead alloy and aluminum tin alloy hard matrix soft particle bearings, a method of depositing another layer of alloy on the bearing surface (with a thickness of 0.02-0.04mm) is adopted, making the bearing a structure of steel back, bearing alloy, and third alloy layer, hence the name "three-layer metal bearing". The main function of the third alloy layer is to improve the anti adhesive bite, compliance, and oleophilicity of hard matrix soft particle bearings, retaining the advantages of hard matrix soft particle alloys and compensating for their disadvantages, thus being widely used. Three layer metal bearings cannot be scraped or brushed, otherwise they will lose the function of the third alloy layer and accelerate the wear of the bearing and journal, resulting in a rapid increase in the fit clearance.
2. Selection and repair of bearings
Due to its special structural characteristics, modern automotive engine sliding bearings should pay attention to the following matters when repairing:
(1) Thin walled bearing shells are not allowed to be repaired or scraped. In the past, when replacing the crankshaft main bearings and connecting rod bearings of car engines with new bearing shells, scraping was necessary to ensure an ideal contact area. In fact, the wear-resistant alloy coating on the crankshaft main bearings and connecting rod bearings of modern automotive engines is very thin, with high dimensional accuracy and low surface roughness values, and generally does not allow for scraping. Can only be selected according to the corresponding size; If there is no suitable size of crankshaft bearing, it is necessary to use the method of base hole grinding to grind the crankshaft to obtain the appropriate fit clearance. In order to adapt to this situation, the method of grinding the journal according to the size of the bearing shell should be adopted, changing the previous method of matching the bearing shell with the shaft. For three-layer alloy bearings, the surface alloy layer is covered by electroplating to improve the surface performance of copper lead alloy bearings. If scraped, this effect will be lost and the original design concept will be destroyed. The previously widely used processes of scraping and bumping tiles should gradually transition towards directly assembling finished tiles.
(2) After the bearing is worn, it is not allowed to add pads on the back of the bearing. The bearing shell and the bearing seat are two separate parts, and when assembled, they work like one part. Due to the thin wall of the bearing shell, in order to ensure the correct geometric shape during operation, it relies entirely on the geometric shape of the bearing seat hole. Therefore, the machining accuracy of the two parts is very high, and the surface roughness value is very low. If paper is placed between them, it will inevitably damage their correct fit. At the same time, paper is a poor conductor of heat, which is not conducive to the heat dissipation of the bearing shell. Therefore, the paper pad may cause the lubrication system oil temperature to be too high, and even cause bearing burning accidents. Similarly, it is not allowed to pad copper under the tile back. In addition, the bearing shell is not allowed to loosen after assembly, and it is easy to loosen after placing something on the back of the bearing shell, which can damage the normal working conditions of the bearing shell.
(3) The positioning lip on the back of the bearing should also prevent rolling of the bearing. The bearing shell requires reliable positioning with the bearing shell seat during operation, and is not allowed to rotate, move, or vibrate. During the overhaul, it was found that the back of the tile was worn very smoothly, indicating that there was looseness. However, the key measure for reliable positioning of the bearing shell is appropriate interference fit, rather than the role of the positioning lip, which is used for initial positioning during assembly.
3. The free elastic force of the bearing must meet the requirements
In order to make the bearing easy to assemble and closely fit with the seat hole, and to prevent the working surface of the bearing cover from wrinkling under pressure after tightening, it is necessary to ensure that the free elastic force of the repaired bearing meets the requirements. The minimum value of free elastic force Z for general thin-walled bearings is 0.25-0.5mm, and the maximum value of Z is 1.20-1.5mm. If the elastic force is too small, it will reduce the adhesion force on the back of the bearing after being installed in the hole method. When tightening the bearing cover, it is easy to cause the low carbon steel metal material on the back of the bearing to slide under pressure and shrink and bulge towards the wear reducing metal side. The shrinkage and protrusion of the bearing will seriously hinder the heat transfer from the bearing to the seat hole, which can easily melt the metal layer and cause a lava accident. Of course, excessive free elastic force can also have adverse effects on the reliability and lifespan of bearings, as the shear stress at the joint between the wear-resistant alloy layer and the bearing back increases, making it easy for the alloy to peel off at the joint.
2026 January 4th Week Marginal Product Recommendation:
MG-1A Aluminum matrix composite bearings：
MG-1A is a composite material of PTFE compound tape on aluminum shell, the PTFE is tape up to 0.20 mm thickness, enabling the bearing can be sized after being fixed, meanwhile the thick PTFE layer isolates noise. The bearing is widely applied in OA machinery, shock absorber for light design bicycle.
