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The crankshaft is the most important part of the engine. It takes the force from the connecting rods and converts it into torque, which is output by the crankshaft and drives other accessories on the engine to work.
The crankshaft is subjected to the combined action of centrifugal force of rotating mass, periodic change of gas inertia force and reciprocating inertia force, so that the crankshaft bears the action of bending and torsional load.
Therefore, the crankshaft is required to have enough strength and stiffness, and the journal surface needs to be wear-resistant, uniform work and good balance.
The crankshaft is the main rotating part of the engine. After the connecting rod is installed, the up and down (reciprocating) movement of the connecting rod can be accepted into a cycle (rotating) movement.
The action of the crankshaft
The crankshaft is the most important part of the engine. It takes the force from the connecting rods and converts it into torque, which is output by the crankshaft and drives other accessories on the engine to work.
The crankshaft is subjected to the combined action of centrifugal force of rotating mass, periodic change of gas inertia force and reciprocating inertia force, so that the crankshaft bears the action of bending and torsional load.
Therefore, the crankshaft is required to have enough strength and stiffness, and the journal surface needs to be wear-resistant, uniform work and good balance.
The crankshaft is the main rotating part of the engine. After the connecting rod is installed, the up and down (reciprocating) movement of the connecting rod can be accepted into a cycle (rotating) movement.
Composition of crankshaft
Crankshaft is mainly made of carbon structural steel or nodular cast iron, there are two important parts: spindle neck, connecting rod neck. The main shaft neck is mounted on the cylinder block, the connecting rod neck is connected with the big head hole of the connecting rod, and the small head hole of the connecting rod is connected with the cylinder piston. It is a typical crank slider mechanism.
Crankshaft lubrication mainly refers to the lubrication of the connecting rod big head bearing bush and crankshaft connecting rod neck and the two fixed points. The rotation of the crankshaft is the power source of the engine and the source power of the whole mechanical system.
How the crankshaft works
Crankshaft is one of the most typical and important parts in the engine. It bears the force from the connecting rod, and turns it into torque through the crankshaft output and drives the other accessories on the engine to work, and drives the auxiliary equipment of the internal combustion engine to work.
The crankshaft is subjected to the combined action of centrifugal force of rotating mass, periodic change of gas inertia force and reciprocating inertia force, so that the crankshaft bears the action of bending and torsional load.
Crankshaft processing technology
Crankshaft spindle neck and connecting rod neck outside milling processing
During the processing of crankshaft parts, due to the influence of the structure of the disc milling cutter itself, the cutting edge and the workpiece are always in intermittent contact with impact. Therefore, the gap link is controlled in the entire cutting system of the machine tool, which reduces the vibration caused by the movement gap during the machining process, thereby improving the machining accuracy and the service life of the tool.
Crankshaft spindle neck and connecting rod neck grinding
The tracking grinding method takes the center line of the spindle neck as the rotation center, and completes the grinding process of the crankshaft connecting rod neck in turn (it can also be used for the spindle neck grinding) by clamping once. The grinding rod journal is realized by CNC controlling the feed of the grinding wheel and the two-axis linkage of the workpiece rotation movement to complete the crankshaft feeding.
The tracking grinding method adopts one clamping and completes the grinding process of crankshaft spindle neck and connecting rod neck successively on a CNC grinder, which can effectively reduce the equipment cost, reduce the processing cost, and improve the machining accuracy and production efficiency.
Crankshaft spindle neck and connecting rod neck fillet rolling machine
The application of rolling machine is to improve the fatigue strength of the crankshaft. According to the statistics, the crankshaft life of nodular cast iron can be increased by 120% ~ 230% after the round corner rolling.
The life of wrought steel crankshaft can be increased by 70% ~ 130% after fillet rolling. The rotary power of rolling comes from the rotation of the crankshaft, which drives the roller in the rolling head to rotate, and the pressure of the roller is implemented by the oil cylinder.
The most common fatigue failure of engine crankshaft is metal fatigue failure, namely bending fatigue failure and torsion fatigue failure, the former is more likely than the latter. Bending fatigue cracks first appear in the connecting rod journal (crank pin) or the round corner of the spindle neck, and then develop to the crank arm.
Torsional fatigue cracks occur at poorly machned oil holes or rounded corners, and then develop in the direction of the axis. The fatigue failure of metals is the result of the variable stress that changes periodically with time. Statistical analysis of crankshaft failure shows that about 80% is caused by bending fatigue.
The main cause of crankshaft fracture
1. Long-term use of oil deterioration, serious overload, overhang, resulting in long-term engine overload operation and burning tile accident. The crankshaft suffered severe wear due to engine shingle burn.
2. After the engine is repaired, the loading has not gone through the running-in period, that is, overload and overhang, and the engine is overloaded for a long time, so that the crankshaft load exceeds the allowable limit.
3. In the repair of the crankshaft, surfacing is used, which destroys the power balance of the crankshaft, and the balance check is not done. The unbalance exceeds the standard, which causes the engine to vibrate more and leads to the fracture of the crankshaft.
4. Due to the poor road condition, the vehicle is seriously overloaded and overhung, the engine often runs inside the torsional vibration critical speed, and the shock absorber failure will also cause the torsional vibration fatigue damage and fracture of the crankshaft.
Notes for crankshaft maintenance
In the process of crankshaft repair, the crankshaft should be carefully checked whether there are cracks, bending, twisting and other defects, and the wear of the spindle and connecting rod bearing bush, to ensure that the clearance between the spindle neck and the spindle bush, the connecting rod journal and the connecting rod bearing bush is within the allowed range.
Crankshaft cracks occur in the transition between the crank arm and the journal at the corner, as well as the oil hole in the journal.
The flywheel operation balance should be ensured when repairing and installing the crankshaft.
The crankshaft should be overhauled after serious accidents such as burning tile and ramming cylinder in internal combustion engine.
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