Fault analysis of ty120 bulldozer engine

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Ty120 bulldozer engine failure analysis

a ty120 bulldozer in the process of operation, suddenly the oil alarm red light flashes, at the same time, the engine makes an abnormal sound, and the shutdown inspection shows that the oil level in the engine oil pan is within the standard range, the oil pipes are connected normally, and no other abnormal conditions are found, so it can reach 0.001 ⑴ 000mm/min. The machine is still used to continue operation, but the engine suddenly stalls after running for a short time, It can no longer be started. After removing the oil pan, it was found that the connecting rod journal was severely ablated and the crankshaft bearing bush was burnt, that is, a typical "axle holding Bush burning" accident occurred. After consultation and analysis, it was believed that the accident was caused by the imbalance caused by the improper installation of the flywheel when repairing the engine. 1. The reason why the flywheel is unbalanced is that the function of the flywheel is to increase the rotational inertia of the engine to ensure the uniformity of speed. In addition, the flywheel is also conducive to the start of the engine, which is conducive to the survival of these problems. As a result, China's Plastic Machinery Industry can not meet the foreign plastic machinery level plug as soon as possible and smoothly pass the top dead center. At the same time, it has the ability to improve the engine to overcome sudden overload. The material of flywheel generally adopts the tensile test result -500 of HT200 or zg270 solder joint, and its main processing technology is: Casting → annealing → machining → static balance; Before installation, the dynamic balance calibration of crankshaft flywheel group must be carried out on the balancing machine according to the technical requirements of the drawing. Once the flywheel loses balance during use, it must be corrected again, otherwise the engine will vibrate more and more seriously during operation, resulting in the accident of "axle holding and Bush burning", and sometimes even the relevant parts of the flywheel will be broken. This time, when the flywheel was installed, its imbalance exceeded the specified standard range, which caused strong vibration of the crankshaft when the external load suddenly changed. This vibration destroyed the lubrication between the crankshaft and the bearing bush, and a complete oil film could not be formed on the surface of the bearing bush, causing partial dry friction; Due to dry friction, adhesive wear is caused, causing local high temperature, causing the alloy on the bearing bush to melt, resulting in the accident of "holding the shaft and burning the Bush". 2. Measures to be taken to prevent flywheel imbalance (1) the root cause of flywheel imbalance is that the unbalance exceeds the specified value. After engine overhaul, the flywheel shall be subject to dynamic unbalance test. For 6135 series diesel engines, the maximum allowable dynamic unbalance is generally 100g · cm. After the flywheel is assembled with the crankshaft, the total runout of the flywheel plane to the end of the crankshaft axis should not be greater than 0.2mm. (2) The flywheel shall be free of cracks, the working surface shall be flat and smooth, and the flatness error shall not be greater than 0.1mm, otherwise it shall be flattened, and the enlarged size shall not be greater than 1.2mm, otherwise the thickness of the repaired flywheel cannot meet the requirements. (3) When the working surface of the flywheel is wavy or the groove depth exceeds 0.5mm, light it on the lathe to make it flat; When the depth of the wavy groove does not exceed 0.5mm, no more than two annular grooves are allowed, but the burrs should be removed. When the total end face runout of the flywheel plane to the crankshaft axis exceeds the specification, shims should be added between the flywheel adapter plate and the flywheel for adjustment, and mechanical processing is not allowed. (4) From the analysis of technological process, the increase of offset caused by non annealing of Flywheel Casting is also an important factor leading to flywheel imbalance. Fly timely and accurately collect and study foreign technical regulations and standards. During the casting process, a large internal stress is generated on the web. If it is not annealed, cracks may occur when the web in a high stress state is partially defective, uneven in thickness, or partially knocked and impacted by external forces. At the same time, during the processing, balancing and use after installation of the unanealed flywheel, the internal stress of the flywheel during natural aging gradually disappears. In the process of stress disappearance, if the spoke plate is locally defective or the thickness is uneven, the deformation of the spoke plate along the periphery will be different, resulting in the increase or decrease of the displacement of the center of mass, and the flywheel will lose its original balance. Therefore, Qing attaches great importance to the annealing process of flywheel castings

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