What are the automotive engine journal bearings?
The automobile engine sliding bearing includes: connecting rod bushing, connecting rod bearing, main bearing and crankshaft thrust bearing and so on. 1. connecting rod bearings and main bearings, connecting rod bearings and main bearing all bear alternating load and high speed friction, therefore, the bearing material must have enough fatigue strength, but also small friction, wear resistance and corrosion resistance. The connecting rod bearing and the main shaft bearing are made up of the upper and lower two plate bearings. Each Bush is composed of steel back and antifriction alloy layer or steel back, antifriction alloy layer and soft coating. The former is called two layer structure bush, and the latter is called three layer structure bush. The back of the steel is the base of the bush. It is made of low carbon steel plate of 1 ~ 3mm thickness to ensure higher mechanical strength. The antifriction alloy layer is cast on the back of the steel, and the antifriction alloy materials are mainly white alloy, copper based alloy and aluminum base alloy.
In the assembly, bearing the circumferential interference into radial interference, the radial pressure generated on the bearing hole of the bearing bush tightly in the bearing hole, to ensure its good bearing and heat capacity, improve the reliability of the bearing and prolong its service life. 2. crankshaft thrust bearings, when the car is running, because of the clutch pedal, the crankshaft is applied to the axial thrust, so that the crankshaft axial movement. Excessive axial movement will affect the normal operation and destruction of the piston connecting rod set, correct timing of the gas distribution and injection timing of the diesel engine. In order to ensure the correct axial alignment of the crankshaft, a thrust bearing is required and only a thrust bearing is provided at one point to ensure that the crankshaft is free to elongate when heated. The crankshaft thrust bearing has 3 forms: flanged bush, half ring thrust plate and thrust bearing ring. The flanging bearing bush is to make the flange on both sides of the Bush as the thrust surface and cast antifriction alloy on the thrust face. There is a clearance of 0.06 ~ 0.25mm between the thrust surface of the Bush and the thrust surface of the crankshaft, thus limiting the axial thrust of the crankshaft. The semicircle ring thrust plate is usually four pieces, each of the upper and lower two pieces are respectively installed in the shallow groove of the body and the main bearing cover, and are positioned with a positioning tongue or a positioning pin to prevent the rotation. When assembling, the thrust surface of the antifriction alloy layer shall be directed toward the thrust surface of the crankshaft, and shall not be reversed. The thrust bearing ring is two pieces of thrust rings which are respectively arranged on both sides of the first main bearing cap.
Also called white alloy Babbitt, tin based white metal used to reduce friction, but low fatigue strength, heat resistance, temperature exceeding 100 DEG C hardness and strength decreased significantly, the gasoline engine used to load. The outstanding advantages of copper lead alloy are its large carrying capacity, high fatigue resistance and good heat resistance. But the running in performance and corrosion resistance are poor. In order to improve its running in and corrosion resistance, a layer of soft metal is usually electroplated on the surface of copper lead alloy into three layers of structural bearings, which are mostly used in high strength diesel engines. Al based alloys include aluminum, antimony magnesium alloy, low tin aluminum alloy and high tin aluminum alloy. High tin aluminum alloy bearings containing more than 20% of tin are widely used in gasoline engines and diesel engines because of their better bearing capacity, fatigue resistance and antifriction performance. The soft coating refers to electroplated a tin or tin lead alloy on the antifriction alloy layer. Its main function is to improve the running in performance of the Bush and to be used as the protective layer of the antifriction alloy layer. When the Bush is in the free state, the distance between the outer ends of the two joint surfaces is larger than the diameter of the bearing bore, and the difference is called the opening of the bearing bush.
