The meaning of crankshaft dynamic balance
Published:
2019-06-29 11:04
The crankshaft is the most important component in an engine in an automobile engine. It takes the force from the connecting rod and converts it into torque through the crankshaft output and drives other accessories on the engine. When the quality of the crankshaft is uniform, the installation is good, and the rotation is stable. At this time, under ideal conditions, the support of the crankshaft hole of the engine block is only subjected to gravity, and the crankshaft moves like a static load only. When the mass distribution of the crankshaft is uneven or improperly installed, the inertia main shaft of the crankshaft does not coincide with the rotary shaft of the rotor, which causes the center of mass of the crankshaft to deviate from the center of rotation. The deviation of the center of mass produces inertial centrifugal forces and centrifugal couples, causing additional rotational loads on the cylinder support.
There are many reasons for the imbalance of the crankshaft:
Design aspect
(1) The geometric shape of the crankshaft rotor is designed with typical asymmetrical structures: such as crank pin, crank arm, oil hole, timing gear and pulley keyway;
(2) 40% of the surface of the finished crankshaft belongs to the unprocessed matte surface (uneven quality surface).
2. There are two kinds of materials, forgings and castings, and the internal structure is uneven.
3. There are two cases of integral and combined crankshafts in terms of manufacturing process:
(1) Processing error causes centroid shift;
(2) assembly causes mass deviation;
(3) When the whole machine is installed, the eccentricity of the bearing causes the rotation axis to shift.
4. Change of balance state during operation The crankshaft is supported by multiple journals in the engine and multiple forces (force of the piston rod), so that the balance state changes.
The engine is the heart of the car, and the crankshaft is a moving part that rotates at high speed in the engine. When the crankshaft is in dynamic unbalanced state, the engine block support bearing is subjected to the fluctuating reaction force caused by the centrifugal inertial force in addition to the normal working load, so that the support and the entire engine are subjected to additional dynamic loads, thereby causing the crankshaft and The friction pair between the main shafts accelerates wear and high frequency fatigue damage. The existence of unbalanced crankshaft causes vibration and noise of the engine and even the whole car, increases energy consumption, affects engine life and working performance, degrades the working environment of the engine, causes resonance and causes instability, and causes damage to the whole machine. Cylinders, flywheel shells, etc. are cracked, causing major accidents. The effects of crankshaft imbalance on vibration and wear were studied. The vibration of the engine was 0.008 mm and 0.09 mm, and the vibration speeds were 1.65 cm/s and 0.85 cm/s, respectively, when the imbalance of the crankshaft was 300 gcm and the unbalance after the balance was 50 gcm. The average wear of the bearing pads was 787 mg and 348 mg, respectively.
With the continuous development of science and technology and the rapid advancement of manufacturing industry, the competition of products is becoming increasingly fierce, and people's requirements and expectations for the performance and quality of products are getting higher and higher. The production of high-performance, high-life, low-energy and pollution-free products (noise is one of the pollution) is the pursuit of the enterprise, so the manufacturing industry pays more and more attention to the balance of the rotor. Balance is an indispensable process in the rotor manufacturing process. The imbalance of the rotor can be corrected by a dynamic balancing machine.
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