Research On The Influence Of Different Balance Rates On Crankshaft Strength And Machine Vibration

With increasingly stringent environmental regulations,the engine is constantly moving towards the direction of lightweight,low energy consumption,low emissions,low noise,and high reliability.Due to the periodicity of the working process of the engine and the periodicity of the movement of the parts,the rotary inertia force,reciprocating inertia force and output torque generated in the operation of the crank-connecting rod mechanism show periodic changes,so the engine has a good balance,which is extremely important to reduce the vibration and noise of the whole machine.Due to the body and crankshaft are not rigid body,the reciprocating inertial force of the crank-connecting rod mechanism and rotation inertia force produced by the crankshaft bending moment can make the crankshaft in the process of our work in a cyclical bending deformation,not only increased the crankshaft bearing load,will cause the vibration of the engine,different balance rate crankshafts have different effects on the vibration of the whole machine.Therefore,studying the influence of crankshaft on the dynamic performance and vibration of the crankshaft system with different balance ratio schemes,optimizing the design of the crankshaft is of great significance for reducing the vibration of the whole machine and improving the reliability and durability of the internal combustion engine.Taking a non-road high-pressure common rail four-cylinder diesel engine as the research object,the system analyzes the balance of four crankshaft solutions with different balance rates and different balance weight structures.The accuracy of the finite element model of crankshaft and crankshaft is verified by modal test and simulation.Based on the theory of flexible multi-body dynamics and elastohydrodynamic lubrication,establishing a multi-body dynamics simulation model for shafting,study the influence of different balance rate of crankshaft on bearing load,main bearing lubrication,crankshaft strength and whole machine vibration under rated working conditions,and the surface vibration response test of the whole machine was carried out.The main research contents and results are as follows:(1)Balance analysis of crankshaft with different balance rateBased on rate calculation principle of moment balance,the balance of different rate of four counterweight and eight counterweight crankshaft internal equilibrium analysis,the results show that the different balance blocks and balance rate can realize the crankshaft dynamic balance and static balance,the rate of 100% balance within eight counterweight crankshaft bending moment smallest,the weight of the heaviest,the rate of 50% balance within four counterweight crankshaft bending moment value maximum,the lightest in weight.(2)Modal parameter analysis of body and crankshaftBy comparing the natural frequencies and modal shapes of the body and crankshaft with the finite element modal calculation,the results show that the error of the body and crankshaft experimental modal is within 5%,which verifies the accuracy of the engine body and crankshaft finite element model.The calculated modal comparisons of the crankshafts of different schemes show that as the equilibrium ratio increases,the mass of the crankshaft increases and the first-order natural frequency decreases.(3)Analysis of main bearing load and lubrication characteristic of the crankshaft with different balance rateUnder the rated speed condition,with the increase of the balance rate,the load peak of the first,third and fifth spindle increases,the average load of each main bearing decreases,and the impact coefficient increases,the impact coefficients of the first main bearing under different crankshaft schemes are 6.66,6.82,9.15 and 9.15 respectively.With the increase of the balance rate,the maximum bearing bending moment of each main bearing increases,and the average bending moment of the first,third and fifth main bearings decreases.Underrated speed condition,different balance ratio crankshaft main bearings are in hydrodynamic lubrication state.With the increase of the equilibrium rate,the first,third,fourth and fifth main bearing film thickness ratio increases,and the maximum oil film pressure and rough contact pressure increase.The 50% balance rate crankshaft has a high peak contact pressure in the fifth main bearing.With the increase of the equilibrium rate,the eccentricity of the first and fifth main bearings decreases.(4)Fatigue strength analysis of crankshaft with different balance rateUnder the rated speed condition,with the increase of the balance rate,the maximum stress value at the rounded corners of the crankshaft increases,the maximum stress value is 284.1MPa,which appears at the rounded corner of crankshaft crank pin with four counterweights and 100% balance rate.At the same balance rate,the maximum stress value of the circular Angle of the eight counterweight crankshaft.With the increase of the balance rate,the fatigue safety factor of the crankshaft fillet decreases,under different crankshaft schemes,the minimum safety coefficient of the rounded corner of the crank pin of the eighth crank arm is 1.93,2.01,1.7 and 1.77,respectively;Under the same balance rate,the minimum safety factor is 1.7,which appears at the rounded corner of the crank pin with a 100% balance rate of four counterweights.(5)Vibration analysis of crankshaft with different balance rateIn the rated speed condition,the vibration of the engine's various points of attention shows that as the balance rate increases,the peak of the vibration acceleration decreases at different harmonic points of the body skirt and the oil sump,the vibration speed level of the point of interest on the body is reduced,and the cylinder head cover and the oil pan are lowered at the vibration speed level in the low frequency band.At 500 Hz,1000Hz and 2000 Hz octave center frequency,the normal vibration velocity level of the engine surface indicates,with the increase of the balance rate,the body vibration speed level decreases,octave center frequency of 500 Hz,the vibration velocity level of cylinder head cover and oil sump increases,octave center frequency of 1000 Hz and 2000 Hz,the vibration velocity level of cylinder head cover and oil sump is reduced;At the same balance rate,octave center frequency of 2000 Hz,and the vibration speed level of the whole balance of the eight balance weight scheme is reduced.