Reduction of drag torque is one of important potentials to improve transmission efficiency.Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the di...Reduction of drag torque is one of important potentials to improve transmission efficiency.Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the difficulty in modeling the flow pattern between two plates.Flow pattern was considered as laminar flow and full oil film in the gap between two plates in traditional model.Subsequent equivalent circumferential degree model presented an improvement in oil film shrinking due to centrifugal force,but was also based on full oil film in the gap,which resulted difference between model prediction and experimental data.The objective of this paper is to develop an accurate mathematical model for the above problem by using experimental verification.An experimental apparatus was set up to test drag torque of disengaged wet clutch consisting of single friction and separate plate.A high speed camera was used to record the flow pattern through transparent quartz disk plate.The visualization of flow pattern in the clearance was investigated to evaluate the characteristics of oil film shrinking.Visual test results reveal that the oil film begins to shrink from outer radius to inner radius at the stationary plate and only flows along the rotating plate after shrinking.Meanwhile,drag torque decreases sharply due to little contact area between the stationary plate and the oil.A three-dimensional Navier-Stokes （N-S） equation based on laminar flow is presented to model the drag torque.Pressure distributions in radial and circumferential directions as well as speed distributions are deduced.The model analysis reveals that the acceleration of flow in radial direction caused by centrifugal force is the key reason for the shrinking at the constant feeding flow rate.An approach to descript flow pattern was presented on the basis of visual observation.The drag torque predicted by the model agrees well with test data for non-grooved wet clutch.The proposed model enhances the precision for predicting drag torque,and lays down a framework on which some subsequent models are developed.展开更多
Reduction of drag torque in disengaged wet clutch is one of important potentials for vehicle transmission improvement. The flow of the oil film in clutch clearance is investigated. A three-dimension Navier-Stokes(N-S)...Reduction of drag torque in disengaged wet clutch is one of important potentials for vehicle transmission improvement. The flow of the oil film in clutch clearance is investigated. A three-dimension Navier-Stokes(N-S) equation based on laminar flow is presented to model the drag torque. Pressure and speed distribution in radial and circumferential directions are deduced. The theoretical analysis reveals that oil flow acceleration in radial direction caused by centrifugal force is the key reason for the shrinking of oil film as constant feeding flow rate. The peak drag torque occurs at the beginning of oil film shrinking. A variable is introduced to describe effective oil film area and drag torque after oil film shrinking is well evaluated with the variable. Under the working condition, tests were made to obtain drag torque curves at different clutch speed and oil viscosity. The tests confirm that simulation results agree with test data. The model performs well in the prediction of drag torque and lays a theoretical foundation to reduce it.展开更多
Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equiva...Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equivalent radius is a function of clutch speed and flow rate. The drag torque achieves its peak at a critical speed. Above this speed, drag torque drops due to the shrinking of the oil film. The model also points out that viscosity and flow rate effects on drag torque. Experimental results indicate that the model is reason-able and it performs well for predicting the drag torque peak.展开更多
The effect of the design parameter on the clutch engagement process of the hydro-mechanical continuously variable transmission(CVT)was investigated.First,the model of the power train was developed with the software of...The effect of the design parameter on the clutch engagement process of the hydro-mechanical continuously variable transmission(CVT)was investigated.First,the model of the power train was developed with the software of SimulationX,and the clutch shift experiment was used to validate the correctness of the model.Then,the friction coefficient function was fitted with the test data to get the friction coefficient model suitable for this paper.Finally,based on the evaluating index of the friction torque and the friction power,two groups of design parameters(oil pressure and friction coefficient)were simulated and explained the changing regulation theoretically.According to the simulation results,the high oil pressure and friction coefficient can reduce the slipping time.The large oil pressure can increase the peak torque but the effect of friction coefficient on the peak torque is not so significant.The friction power reaches the maximum value at 3.2 s,the peak value increases as the oil pressure and friction coefficient increase.The effect of the oil pressure on the clutch engagement and thermal performance is greater than the friction coefficient.展开更多
Wet clutch is an important shifting component in automatic transmission,and its properties will affect the gear shift performance. By comparing the calculated and test results,the static friction torque model was prov...Wet clutch is an important shifting component in automatic transmission,and its properties will affect the gear shift performance. By comparing the calculated and test results,the static friction torque model was proved to be capable of describing the real pressure and torque only in the situation of high-energy engagement.Therefore,a dynamic torque model was proposed on basis of hydrodynamic properties between friction surfaces, in which the clutch engagement was divided into three phases for hydrodynamic lubrication, mixed lubrication, and mechanical contact. The proposed dynamic torque model was validated by comparing the calculated and test results. The effects of temperature,pressure,and pressure changing rate of automatic transmission fluid( ATF) on the clutch torque were analyzed. Based on these results,the clutchto-clutch torque control during shifting in automatic transmission was optimized,and as a result,the shifting comfort was significantly improved since the problems such as the fluctuation and sudden drop of the engine rotating speed during shifting were eliminated.展开更多
Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of e ciency improvement. Aeration of oil film between two closely rotating plates promotes...Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of e ciency improvement. Aeration of oil film between two closely rotating plates promotes the decrease of drag torque at high speed region. The e ects of surface tension and static contact angles during aeration are nonnegligible showed by test results. The traditional lubrication model does not adequately predict the experimental results with di erent surface tension and contact angles during aeration. Hence, in this present paper, contact angles between Aluminum and Teflon materials were firstly measured, and the drag torques under two di erent contact angles were examined experimentally. An improved lubrication model of drag torque based on Navier–Stokes equations at the gas-liquid interface was built. The lubrication boundary condition was modified to introduce the e ects of surface tension and contact angle. The model shows that the e ects at the beginning of aeration of oil film are significant. These e ects almost occur at stationary plate due to low Reynolds number and Weber number. The model shows that an increase in the surface tension promotes aeration, but does not a ect the peak drag torque. Increasing contact angle also promotes the aeration, and accelerates the decrease of drag torque. The larger contact angle is, the smaller the peak drag torque will be. A computational fluid dynamics(CFD) model based on volume of fluid(VOF) method was presented to validate the interface shape when aeration occurs. The model prediction has a good agreement with experimental observations for Aluminum plates and Teflon plates. The modified lubrication model of drag torque gives a convenient description of the e ects of surface tension and contact angel, and lays down a frame to understand the beginning of aeration.展开更多
Traditional mathematical models cannot predict and explain the phenomenon by which the drag torque(DT)in wet clutches rises in the high-speed zone.In order to evaluate the DT in such conditions,a two-phase air-fluid m...Traditional mathematical models cannot predict and explain the phenomenon by which the drag torque(DT)in wet clutches rises in the high-speed zone.In order to evaluate the DT in such conditions,a two-phase air-fluid mathematical model for a DT with grooves was elaborated.The mathematical model was based on the theory of viscous fluid flow.A two-phase volume of fluid model was also used to investigate the distribution and volume fraction of air and fluid.Experiments on three friction plates with different grooves were conducted to validate the resulting mathematical model.It was found that the gap between plates decreased in the high-speed zone,thereby producing an increase of the DT in the high-speed zone.These results support the understanding of the physical phenomena relating to disengaged wet clutches,and provide a theoretical basis for the future improvement of drive systems.展开更多
A mathematical model was developed to analyze the characteristics of the wet clutch during engagement. The lubricant squeeze action was simulated with Patir and Cheng average flow model in which the permeability of fr...A mathematical model was developed to analyze the characteristics of the wet clutch during engagement. The lubricant squeeze action was simulated with Patir and Cheng average flow model in which the permeability of friction material is taken into account, and the asperity load is calculated according to the Greenwood and Tripp approach. In this model, effects of friction material permeability, applied load and driving velocity on the engagement characteristics of the wet clutch were studied. The results show that friction material with high permeability reduces the film thickness rapidly and increases the torque peak; the applied load increases the asperity contact pressure and the friction torque, and reduces the engagement time; the driving velocity mainly increases the engagement time. The theoretical torque and relative velocity curves agree qualitatively with the experimental ones, which verifies the wet clutch engagement model.展开更多
This paper aims to investigate the effect of porosity percentage on the wear performance of a wet clutch. A wear calculation model for the relationship of porosity and wear mass loss is established. The results of exp...This paper aims to investigate the effect of porosity percentage on the wear performance of a wet clutch. A wear calculation model for the relationship of porosity and wear mass loss is established. The results of experiments conducted verify the wear coefficient expression used in the model. The influence of porosity on the wear performance of a friction disc was also analyzed for various pressures and speeds. Specifically,the 80 min sliding test was performed with three different friction disc porosity percentages using a wet clutch test rig. Comparison of the model calculation results with the measured values confirmed the accuracy of the calculation model. The test results show that the calculated and detected data fit well,which indicates that the wear calculation model can be used to estimate the wear mass loss of wet clutch friction plates. These research results will help to improve the anti-abrasion properties and employment lifespan of wet clutch friction discs.展开更多
The impacts of different groove shapes, numbers, and angle of friction dish on transmitting torque, speed, push pressure in wet speeding clutch are discussed in this paper. Since the wet speed governing clutch works w...The impacts of different groove shapes, numbers, and angle of friction dish on transmitting torque, speed, push pressure in wet speeding clutch are discussed in this paper. Since the wet speed governing clutch works within hydrodynamic lubrication, mixture lubrication, boundary lubrication and contact situation, the oils combining with α hydrocarbon or polyester are getting widely used as lubricant. The power law fluid model with Patir Cheng average flow model, GT asperity contact model and oil film inertia are applied for average Reynolds equation setting. In order to investigate the relationship between average push pressure within hydrodynamic lubrication and mixture lubrication, average transmitting torque and output speed, the numeral calculation and analysis are presented. According to calculation, it is found that the groove shape, groove angle and groove numbers affect the average transfer torque and push pressure with the speed rate.展开更多
基金supported by National Defense Arming Pre-researching Project of China(Grant No.40402060102)
文摘Reduction of drag torque is one of important potentials to improve transmission efficiency.Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the difficulty in modeling the flow pattern between two plates.Flow pattern was considered as laminar flow and full oil film in the gap between two plates in traditional model.Subsequent equivalent circumferential degree model presented an improvement in oil film shrinking due to centrifugal force,but was also based on full oil film in the gap,which resulted difference between model prediction and experimental data.The objective of this paper is to develop an accurate mathematical model for the above problem by using experimental verification.An experimental apparatus was set up to test drag torque of disengaged wet clutch consisting of single friction and separate plate.A high speed camera was used to record the flow pattern through transparent quartz disk plate.The visualization of flow pattern in the clearance was investigated to evaluate the characteristics of oil film shrinking.Visual test results reveal that the oil film begins to shrink from outer radius to inner radius at the stationary plate and only flows along the rotating plate after shrinking.Meanwhile,drag torque decreases sharply due to little contact area between the stationary plate and the oil.A three-dimensional Navier-Stokes （N-S） equation based on laminar flow is presented to model the drag torque.Pressure distributions in radial and circumferential directions as well as speed distributions are deduced.The model analysis reveals that the acceleration of flow in radial direction caused by centrifugal force is the key reason for the shrinking at the constant feeding flow rate.An approach to descript flow pattern was presented on the basis of visual observation.The drag torque predicted by the model agrees well with test data for non-grooved wet clutch.The proposed model enhances the precision for predicting drag torque,and lays down a framework on which some subsequent models are developed.
基金supported by National Defense Arming Pre-researching Project(Grant No. 40402060102)
文摘Reduction of drag torque in disengaged wet clutch is one of important potentials for vehicle transmission improvement. The flow of the oil film in clutch clearance is investigated. A three-dimension Navier-Stokes(N-S) equation based on laminar flow is presented to model the drag torque. Pressure and speed distribution in radial and circumferential directions are deduced. The theoretical analysis reveals that oil flow acceleration in radial direction caused by centrifugal force is the key reason for the shrinking of oil film as constant feeding flow rate. The peak drag torque occurs at the beginning of oil film shrinking. A variable is introduced to describe effective oil film area and drag torque after oil film shrinking is well evaluated with the variable. Under the working condition, tests were made to obtain drag torque curves at different clutch speed and oil viscosity. The tests confirm that simulation results agree with test data. The model performs well in the prediction of drag torque and lays a theoretical foundation to reduce it.
基金Sponsored by the Ministerial Level Advanced Research Foundation(10506024)
文摘Considering the surface tension effect and centrifugal effect, a mathematical model based on Reynolds equation for predicting the drag torque of disengage wet clutches is presented. The model indicates that the equivalent radius is a function of clutch speed and flow rate. The drag torque achieves its peak at a critical speed. Above this speed, drag torque drops due to the shrinking of the oil film. The model also points out that viscosity and flow rate effects on drag torque. Experimental results indicate that the model is reason-able and it performs well for predicting the drag torque peak.
基金Project(CX(19)3081)supported by the Agricultural Science and Technology Independent Innovation Fund of Jiangsu Province,ChinaProject(BE2018127)supported by the Key Research and Development Program of Jiangsu Province,China。
文摘The effect of the design parameter on the clutch engagement process of the hydro-mechanical continuously variable transmission(CVT)was investigated.First,the model of the power train was developed with the software of SimulationX,and the clutch shift experiment was used to validate the correctness of the model.Then,the friction coefficient function was fitted with the test data to get the friction coefficient model suitable for this paper.Finally,based on the evaluating index of the friction torque and the friction power,two groups of design parameters(oil pressure and friction coefficient)were simulated and explained the changing regulation theoretically.According to the simulation results,the high oil pressure and friction coefficient can reduce the slipping time.The large oil pressure can increase the peak torque but the effect of friction coefficient on the peak torque is not so significant.The friction power reaches the maximum value at 3.2 s,the peak value increases as the oil pressure and friction coefficient increase.The effect of the oil pressure on the clutch engagement and thermal performance is greater than the friction coefficient.
基金National Science and Technology Support Program,China(No.2011BAG09B00)
文摘Wet clutch is an important shifting component in automatic transmission,and its properties will affect the gear shift performance. By comparing the calculated and test results,the static friction torque model was proved to be capable of describing the real pressure and torque only in the situation of high-energy engagement.Therefore,a dynamic torque model was proposed on basis of hydrodynamic properties between friction surfaces, in which the clutch engagement was divided into three phases for hydrodynamic lubrication, mixed lubrication, and mechanical contact. The proposed dynamic torque model was validated by comparing the calculated and test results. The effects of temperature,pressure,and pressure changing rate of automatic transmission fluid( ATF) on the clutch torque were analyzed. Based on these results,the clutchto-clutch torque control during shifting in automatic transmission was optimized,and as a result,the shifting comfort was significantly improved since the problems such as the fluctuation and sudden drop of the engine rotating speed during shifting were eliminated.
基金Supported by National Natural Science Foundation of China(Grant No.51305032)
文摘Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of e ciency improvement. Aeration of oil film between two closely rotating plates promotes the decrease of drag torque at high speed region. The e ects of surface tension and static contact angles during aeration are nonnegligible showed by test results. The traditional lubrication model does not adequately predict the experimental results with di erent surface tension and contact angles during aeration. Hence, in this present paper, contact angles between Aluminum and Teflon materials were firstly measured, and the drag torques under two di erent contact angles were examined experimentally. An improved lubrication model of drag torque based on Navier–Stokes equations at the gas-liquid interface was built. The lubrication boundary condition was modified to introduce the e ects of surface tension and contact angle. The model shows that the e ects at the beginning of aeration of oil film are significant. These e ects almost occur at stationary plate due to low Reynolds number and Weber number. The model shows that an increase in the surface tension promotes aeration, but does not a ect the peak drag torque. Increasing contact angle also promotes the aeration, and accelerates the decrease of drag torque. The larger contact angle is, the smaller the peak drag torque will be. A computational fluid dynamics(CFD) model based on volume of fluid(VOF) method was presented to validate the interface shape when aeration occurs. The model prediction has a good agreement with experimental observations for Aluminum plates and Teflon plates. The modified lubrication model of drag torque gives a convenient description of the e ects of surface tension and contact angel, and lays down a frame to understand the beginning of aeration.
基金support from the research project of basic product innovation of MIIT(VTDP3203).
文摘Traditional mathematical models cannot predict and explain the phenomenon by which the drag torque(DT)in wet clutches rises in the high-speed zone.In order to evaluate the DT in such conditions,a two-phase air-fluid mathematical model for a DT with grooves was elaborated.The mathematical model was based on the theory of viscous fluid flow.A two-phase volume of fluid model was also used to investigate the distribution and volume fraction of air and fluid.Experiments on three friction plates with different grooves were conducted to validate the resulting mathematical model.It was found that the gap between plates decreased in the high-speed zone,thereby producing an increase of the DT in the high-speed zone.These results support the understanding of the physical phenomena relating to disengaged wet clutches,and provide a theoretical basis for the future improvement of drive systems.
基金Funded by the Innovation Foundation of Beijing University of Aeronautics and Astronautics for PhD Candidates
文摘A mathematical model was developed to analyze the characteristics of the wet clutch during engagement. The lubricant squeeze action was simulated with Patir and Cheng average flow model in which the permeability of friction material is taken into account, and the asperity load is calculated according to the Greenwood and Tripp approach. In this model, effects of friction material permeability, applied load and driving velocity on the engagement characteristics of the wet clutch were studied. The results show that friction material with high permeability reduces the film thickness rapidly and increases the torque peak; the applied load increases the asperity contact pressure and the friction torque, and reduces the engagement time; the driving velocity mainly increases the engagement time. The theoretical torque and relative velocity curves agree qualitatively with the experimental ones, which verifies the wet clutch engagement model.
基金supported by the National Natural Science Foundation (No. 51605035)completed with support from the Beijing Finance Fund for Science and Technology Planning project (Nos. KZ201611232032 and KM201611232004)
文摘This paper aims to investigate the effect of porosity percentage on the wear performance of a wet clutch. A wear calculation model for the relationship of porosity and wear mass loss is established. The results of experiments conducted verify the wear coefficient expression used in the model. The influence of porosity on the wear performance of a friction disc was also analyzed for various pressures and speeds. Specifically,the 80 min sliding test was performed with three different friction disc porosity percentages using a wet clutch test rig. Comparison of the model calculation results with the measured values confirmed the accuracy of the calculation model. The test results show that the calculated and detected data fit well,which indicates that the wear calculation model can be used to estimate the wear mass loss of wet clutch friction plates. These research results will help to improve the anti-abrasion properties and employment lifespan of wet clutch friction discs.
文摘The impacts of different groove shapes, numbers, and angle of friction dish on transmitting torque, speed, push pressure in wet speeding clutch are discussed in this paper. Since the wet speed governing clutch works within hydrodynamic lubrication, mixture lubrication, boundary lubrication and contact situation, the oils combining with α hydrocarbon or polyester are getting widely used as lubricant. The power law fluid model with Patir Cheng average flow model, GT asperity contact model and oil film inertia are applied for average Reynolds equation setting. In order to investigate the relationship between average push pressure within hydrodynamic lubrication and mixture lubrication, average transmitting torque and output speed, the numeral calculation and analysis are presented. According to calculation, it is found that the groove shape, groove angle and groove numbers affect the average transfer torque and push pressure with the speed rate.
