Research On Vibration Characteristic Of Tractor-Implement System And Implement Absorption Technology

In the condition of road transportation,the influence of implement on ride comfort and safety of tractor+implement system is great.When the tractor+implement system travels with a high speed in the rough country road,due to the severe vibration of the system,the static load of the guide wheel decreases and the steering stability becomes poor,it is easy to cause the accident.To decrease the vibration of the tractor+implement system in the transportation condition,it is necessary to design the implement absorption system.The vibration characteristic of the tractor+implement system is the foundation of designing the implement absorption system.Therefore,researching the influence of implement on the vibration characteristics of the tractor+implement system and designing the implement absorption as the active damping device,it has the important theoretical significance and engineering application value to improve the ride comfort and driving safety.Taking the CF700 tractor as the research object,on the basis of theory analysis,combining the method of simulation with test verification,the influence of the implement on the vibration characteristics of the tractor+implement system in the condition of road transportation was studied.The implement absorption system was designed and the vibration characteristics of the tractor+implement absorption system was analyed in theory.The vibration characteristics of the tractor+implement absorption system was studied with the combination of the different stiffness and damping.The stiffness and damping parameters of the implement absorption system were optimized.It is verified that the implement absorption system can improve the vibration characteristics of the tractor.The completed work and achieved results are generalized as follows:1.Taking the CF700 tractor as the research object,the tractor 2-DOF vibration model with a rear mounted implement was established.The structural parameters,the mass attribute parameters and the tyre parameters were obtained by theoretical calculation.By analyzing the vibration characteristics of the system,the calculation formula of the natural frequency and the frequency response function were derived.The variation curve of the natural frequency and the amplitude frequency characteristic curve of the system centroid in vertical vibration,pitch vibration and roll vibration were obtained.The acceleration calculation formulas of the vertical,pitch and roll direction in seat position and the tyre dynamic load coefficient calculation formula were derived.The dangerous driving speed of the system was studied to derive the calculation formula of the dangerous driving speed and obtain the different implement mass.2.The road excitation model of the rural road and the 100 meters relatively smooth runway were established.The random elevation of the rural road was obtained with the tire rolling method.Processing the measuring data to get the roughness and displacement power spectrum density.In the spatial frequency range,the amplitude of PSD at long wavelength was obviously higher than short wavelength,this indicated that long wavelength was related with high amplitude of profile while short wavelength was accompanied by small amplitude.The energy of the amplitude in the surface profile was contributed by the long wavelength.In the lower spatial frequency range between 0.04m-1 and 1.1m-1,the peak of PSD curve is obvious.Because the lower natural frequency of the spring mass,the excitation corresponding to short wave(high frequency input)can effectively be isolated,while the excitation corresponding to long wave(low frequency input)easily causes the resonance of the tractor.The rural road and 100 meters GB pavement are equivalent to the D grade pavement in the grading standards of road.3.The tractor 3-DOF vibration simulation model with a rear mounted implement was established.In different speed,changing the implement's mass,carrying on the simulation using the Matlab software to obtain the simulation data.The peak frequency of the three direction in seat position and the respective natural frequencies are basically same.In same speed,the acceleration RMS of seat in vertical,pitch and roll direction decreases with the increase of the implement mass.The vertical acceleration reduces to 1.064m/s2 from 2.716m/s2,the pitch angle acceleration reduces to 0.907rad/s2 from 2.578rad/s2 and the roll angle acceleration reduces to 0.981rad/s2 from 2.658rad/s2.The front tire's dynamic load coefficient increases with the increase of the implement mass in same speed.It increases to 0.353 from 0.076.Compared with the front tire's dynamic load coefficient,the rear tire's dynamic load coefficient is much smaller.The speed is slow,the rear tire's dynamic load coefficient decreases slightly with the increase of the implement mass and reduces to 0.045 from 0.058,the speed is fast,the rear tire's dynamic load coefficient increases gradually with the increase of the implement mass and increases to 0.194 from 0.058.4.The vibration test system of the tractor+implement was constructed and acceleration signals in time domain were measured.Processing the data to obtain the acceleration power spectral density in the center of mass,the acceleration RMS in seat position and tire dynamic load coefficient.The test result showed that the influence of implement's mass on vibration characteristics of tractor+implemnt system was consistent with the simulation result.The acceleration RMS in seat position and the tire dynamic load coefficient are bigger than the simulation result.The maximum value of the test acceleration RMS and the simulation acceleration RMS's relative error is 15.55%in seat position,the minimum value is 0.80%.The maximum value of the test tire dynamic load coefficient and the simulation result's relative error is 20%,the minimum value is 0%.The errors are in an acceptable range and have a better consistency.5.The three point implement absorption system was designed and the kinetics model of implement absorption system was built.The frequency response function,the formula of the acceleration RMS in seat position and tire dynamic load were derived.6.The range of the implement absorption system's stiffness and damping was determined.The tractor vibration simulation model with implment absorption system was established.The influence of the absorption system's stiffness and damping on the vibration response was analyzed by simulation.The multi-objective optimization mathematical model of the index for the vertical acceleration,the pitch angle acceleration,the front wheel and rear wheel dynamic load coefficient was established.The implement absorption system's stiffness and damping was optimized by unified objective function method.The vertical acceleration RMS and the pitch angle acceleration RMS are respectively reduced by 15.29%and 19.47%.The front wheel and rear wheel dynamic load coefficient are respectively reduced by 40.74%and 42.86%.It can effectively improve the tractor ride comfort and driving safety.