| Based on the high torque and low noise index of modern forestry shrub cutting equipment,and the requirements of complex forest environment,it’s urgent to improve the integrated functions such as cutting efficiency,cutting quality,collection and bundling,which makes it urgent to improve the dynamic characteristics,bearing capacity and service life of gear transmission system of shrub cutting equipment.The time-domain alternating working condition of cutting shrub leads to the correlation of factors such as load distribution between teeth,gear meshing in and out impact and gear machining error,which aggravates the sudden variation of gear load,especially under heavy load and high torque working conditions,resulting in strong impact and vibration of gear,and even scuffing failure of thermoelastic characteristics.The two-stage power branch planetary compound transmission system(TPCT)is an important part of the cutting transmission device.The whole system is composed of parallel shaft gear train and straight tooth planetary gear train.The complexity of the two-stage dynamic characteristics of the cutting transmission device is greater than that of the first stage?It hasbetter bearing performance,greater transmission ratio and higher reliability.This paper mainly takes the cutting transmission gear system as the research object,and analyzes the dynamic characteristics of the cutting transmission gear system in time domain and the thermoelastic behavior of the alternating meshing tooth surface.The research results have important theoretical and practical significance for mastering the anti-scuffing bearing performance and anti-scuffing optimization design of the complex cutting transmission gear system.Firstly,this paper is based on a pre-designed rectangular coordinate shrub cutting device based on intelligent integrated system,which can realize main functions such as high efficient cutting shrub,image directional identification of fixed points,planning and avoiding reserved path,follow-up pick-up and collection of shrub strips,binding and throwing of shrub.The nonlinear factors such as the time-varying phase angle of star gears,the time-varying meshing stiffness of gear pair,the comprehensive meshing error,the system damping and the nonmeshing of gear teeth in the planetary gear train of cutting transmission device of shrub cutting machine are considered,the dynamic characteristic model of all levels of gear train structure in fixed coordinate system is established,and analyzed the meshing elastic deformation conditions of gear pairs at all levels.The non-linear dynamic characteristic model of the whole system is built by using the lumped parameter method,meshing stiffness and meshing error excitation of each gear pair are determined.The time-varying meshing stiffness and meshing comprehensive error(described by meshing line increment)of the secondary power branch spur gear pair during the whole meshing process are analyzed,which provides precondition for gear system dynamic characteristic analysis of cutting and irrigation transmission.Based on the modal analysis of equidistant arrangement and non equidistant arrangement(star gear/planetary gear),the vibration modes of star gear under natural frequencies of 1252.9Hz and 6645.5Hz are consistent with those of equidistant arrangement.The natural frequencies are 920.5Hz and 2488.5Hz,and the vibration modes are the result of 90 degrees rotation of equidistant vibration modes;The natural frequency with two double roots of the planetary gear 489.6Hz is separated into two single roots of 472.2Hz and 498.8Hz,and the vibration mode no longer conforms to the characteristic law of equal spacing arrangement.Secondly,the calculation model of parameter influence degree of TPCT is established,the influence degree of gear engagement rigidity and natural frequency of torsional rigidity of secondary connecting shaft are studied,and the influence law of parameter change on natural frequency of vibration modes is obtained.The modal transition phenomenon of TPCT is analyzed,and the natural frequency is revealed.The time-varying law of natural frequency mode transition under different vibration modes lays a theoretical foundation for revealing its dynamic behavior and phase tuning damping as well as the influence degree of key parameters;the parameter influence degree of natural frequency of TPCT and the vibration mode change characteristics of each substructure are studied,and the engagement rigidity of natural frequency and vibration mode to each gear pair is analyzed.As well as the influence degree of second-stage torsional stiffness,the influence degree of each sub-structure parameter on natural frequency of gear system is obtained.The influence of second-stage torsional stiffness on natural frequency of star gear system under vibration mode and coupling vibration mode is analyzed,and the characteristic mode change law of TPCT is obtained.Among them,the natural frequency curves of modes(12,13)and modes(15,16),which both correspond to a weight of 2,are in the vicinity and undergo a modal change;the natural frequency curves of modes(12,13)and mode 8 intersect,both of which verify their corresponding modal change criteria.Finally,based on the relations between the strength of the cutting sample and its physical and mechanical properties(The combined force on the output shaft when obtaining the maximum load of the gear train is 138.1-146.3N),as well as the heat transfer among the substructures in the gear system,the heat transfer network,heat transfer relationship and heat flow balance equation of gear system of cutting and irrigation transmission are determined according to heat network method.Considering temperature distribution under different cutting and irrigation conditions,the corresponding data of steady state temperature field at each important position of gear system are obtained and compared.Through closed power flow gear drive test stand and thermocouple temperature measuring system,gear meshing process is carried out.The temperature of gear tooth surface is monitored in real time.The measured data of gear tooth surface temperature under different cutting and irrigation conditions are collected and analyzed and compared with the corresponding theoretical calculation results.The error range is controlled within 5%.The two results are quite close,which verifies the correctness of the aforementioned theoretical theories in the paper. |
