The crankshaft journal is the part of the crankshaft that is brighter and rotates with the shaft shank, including the connecting rod journal and main journal.
The role of the crankshaft journal is to transform the gas pressure from the piston connecting rod group into torque for external output, and drive the gas distribution mechanism and other auxiliary devices. Most of them are made of high quality medium carbon steel, medium alloy carbon steel or ductile iron casting. The structure of crankshaft includes front end shaft, main journal, connecting rod journal, crank, balance weight, rear end shaft, etc. And there are oil channels running through the main journal, crank and connecting rod journal in it to lubricate the main journal and connecting rod journal. Since it is subject to various forces in use, there is a certain amount of wear, and different parts have different wear characteristics.
The wear of the main journal along the axial direction should be uniform, and the wear amount of its radial direction is uneven, and a slight ovalness will appear. As the middle journal tends to be under greater force, its wear amount is often larger than that of the two ends. The radial wear of the main shaft tile corresponds to that of the main journal, and the biggest wear part is on the lower bearing, and the wear of the middle shaft tile is larger than that of the two ends.
The radial wear of the connecting rod journal and bearing is uneven, and the wear on its inner side is larger. Uneven wear makes the connecting rod journal form a certain ellipse along the radial direction, and the axial direction is generally uniform wear. The use of large end structure asymmetrical connecting rod due to its connecting rod journal load distribution is not uniform, wear will become conical; the use of symmetrical large end structure of the connecting rod, if the bending will also cause the same consequences.
The biggest part of the connecting rod journal wear, generally in the inner surface of each journal, that is, by the side of the crankshaft centerline, so that the journal loss of round; and wear into a conical part, generally in the lube channel impurities attached to the side and the part of the large force.
Crankshaft journal wear can be measured using a micrometer, crankshaft short journal wear to test the roundness error, the long journal must test the roundness and cylindricity error. The specific measurement method is: each journal to take two sections, each section to take two points. Half of the difference between the maximum and minimum diameter of the same section is the roundness error; half of the difference between the maximum and minimum diameter of the two sections is the cylindricity error. Under normal working conditions, the crankshaft wear is extremely small, generally not more than 0.01mm, cylindricity is less than 0.0025mm.
Crankshaft journals are commonly damaged in the form of journal wear, cracks, burns, bending or fracture, etc. We can analyze the working condition of the engine and the cause of damage from the crankshaft journal wear state. For example, the crankshaft journal wear is too large, the shaft tile even leaks out of the bottom, this situation is generally caused by poor lubrication, oil pressure is too low, oil does not meet the use of the requirements; crankshaft cylindrical oversized, indicating that the engine works under heavy load for a long time; crankshaft burns, blue, holding dead, must be caused by poor lubrication, the most common is the lack of oil.