| The wet friction clutch is widely used in the ship with diesel engine and fixed pitch propeller because of the character of sliding friction which meets the load demand of the fixed pitch propeller.In the process of jointing,there is a rotational speed difference between the input and output ends of the friction clutch;under the action of operating oil pressure,the multiple groups of friction elements-the friction disc and dual steel disc,installed alternately in the clutch,are compressed and produce relative sliding.Because of the force of the sliding,the rotational speed difference between the input and output ends of the clutch gradually approaches to zero,and the motion and torque are transferred from the input end to the output end.A large amount of friction heat will be generated in this process,which leads to a rise in the temperature of the friction elements.With the increase of the rotating speed of the fixed pitch propeller,the torque becomes bigger and bigger,leading to more and more friction heat.The material properties of the friction material and the steel disc get changed with the increase of the temperature.Under the combined action of the external pressure stress and the internal thermal stress,the phenomena of thermal expansion,ablation deformation,wear and tear are produced,which results in the failure work of the friction elements.In the design of friction clutch,not only the steady-state torque transmission ability of friction components,but also the heat load bearing capacity of friction components when they are connected should be considered.Giving full play to the heat load bearing capacity of friction components can effectively shorten the diameter of friction components,reduce the weight of clutch body,increase the rotate speed of clutch,and finally improve the power density of friction clutch.The research of this paper are derived from the Research Project of Marine Power Foundation(MG0501).Aiming at the friction elements of a certain wet friction clutch,the following points have been studied:(1)The simplified dynamic model of the friction clutch is established,assuming that the sliding friction work of the friction element is all converted into friction heat during the jointing process,then the calculation formulas sliding work of friction disc and dual discs isconcluded.The thermal distribution coefficient is obtained by the material properties of the friction elements and the average temperature rise is calculated.The heat dissipation coefficient between the friction element and the cooling lubricating oil is calculated by the oil-liquid characteristics.The friction coefficient is calculated by test parameters.(2)To simplify the structure of friction disc and dual steel disc reasonably,ignore the internal and external spline,friction surface groove and heat dissipation condition,establish the contact model of friction elements through ABAQUS finite element analysis software.Directly apply the parameters like rotational speed and pressure to the model,using the software to simulate the whole process of compressing the friction disc and dual steel disc which causing relative sliding and a rise temperature,then analyze the temperature field and stress field of the simulation results,explore the position and reason of the highest temperature of friction element,so as to look for the failure mechanism of the friction elements,and confirm the evaluation index of the allowable thermal load;modify the infection of rotational speed,pressure,friction element thickness and other parameters to the maximum temperature of the friction elements.The allowable thermal load evaluation index is determined by the failure mechanism of friction element.The influence of rotational speed,oil pressure,sliding time and friction element thickness on the maximum temperature is analyzed by comparison and simulation.The recommended thickness of steel sheet is given by temperature rise coefficient.(3)The model is optimized,the structure size of the model is modified according to the actual situation,the boundary condition is loaded for the model according to the working condition,and the failure and allowable thermal load of friction elements are predicted according to the simulation results.(4)The limit heat load test bench of friction clutch friction element is set up using braking method.By increasing the speed of inertial rotor,the thermal load of friction element is increased until the friction element is ineffective,and the working state of friction element is inferred by calculation the friction coefficient by the test data,and then the allowable thermal load of friction element is determined.The test results are compared with the simulation results to verify the reliability of the simulation model. |
PDF Full Text Request