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)eq...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
Wet multi-plate clutches are relevant components of modern drivetrain applications,not only in terms of function but also safety and comfort.Especially at the beginning of their lifetime,distinct changes of the fricti...Wet multi-plate clutches are relevant components of modern drivetrain applications,not only in terms of function but also safety and comfort.Especially at the beginning of their lifetime,distinct changes of the friction behavior may occur and make the actuation of the clutch challenging.This transcript describes the typical running-in behavior of wet multi-plate clutches and gives a general definition for running-in of clutches.Moreover,a new test method to systematically investigate the running-in behavior of clutches is introduced.This test method contains a test procedure to characterize the running-in behavior on different load levels.Furthermore,a multi-stage procedure to evaluate and characterize the running-in behavior of clutches with mathematical approaches and new characteristic values is given.The quality of the test method is demonstrated on the example of three different tribological systems from dual clutch transmissions(DCT)and automatic transmissions(AT)application using paper friction linings.展开更多
A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphr...A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphragm spring introduces unstable dynamics which becomes more intensive due to the preload spring. In order to explore the intensified unstability, this paper builds dynamic models for the rotating lever coupling a negative stiffness diaphragm spring and a preload spring. The stability analysis using the Routh-Huiwitz criterion shows that the open-loop system can never be stable due to the negative stiffness. Even if the diaphragm spring stiffness is positive, the system is still unstable when the preload of the spring exceeds an upper limit. A proportionalintegral-derivative(PID) closed-loop scheme addressing this problem is designed to stabilize the system. The stability analysis for the closed-loop system shows that stable region emerges in spite of the negative stiffness; the more the negative stiffness is, the less the allowed preload is. Further, the influences of the dimensions and PID parameters on the stability condition are investigated. Finally, the transient dynamic responses of the system subjected to disturbance are compared between the unstable open-loop and stabilized closed-loop systems.展开更多
The brain is among the most energetically costly organs in vertebrates,and thus trade-offs have been hypothesized to exert constraints on brain size evolution.The energy trade-off hypothesis(ETH) predicts that reducin...The brain is among the most energetically costly organs in vertebrates,and thus trade-offs have been hypothesized to exert constraints on brain size evolution.The energy trade-off hypothesis(ETH) predicts that reducing the energy consumption of reproduction or other costly tissues should compensate for the cost of a large brain.Egg production in birds requires a large proportion of the total energy budget,and a clutch mass in some bird species can outweigh the body mass of the female.To date,this hypothesis has mainly been tested in mammals and ectothermic animals such as anurans and fishes.We collated data on adult brain size,body mass and eggproduction traits such as clutch size,egg mass and annual broods from published studies,and conducted a phylogenetic comparative test of the interplay between egg-production investment and brain size evolution across bird species.After controlling for phylogenetic relationships and body size,we find a negative correlation between brain size and clutch size across 1395 species,which favored ETH.However,when egg mass was integrated in models,positive associations were detected between brain size and mass of eggs(via egg mass,clutch mass and annual total egg mass).Our results suggest that brain size trades off against egg-production only via certain aspects(e.g.,clutch size).By contrast,a positive relationship between brain size and total egg reproduction(e.g.,clutch mass and annual total egg mass) implied increased total energy budget outweighing energy allocation across bird species.Our study shows that there is no general energy trade-off between brain size and eggreproduction investment,and suggests that brain size evolution follows mixed strategies across bird species.展开更多
The diaphragm spring clutch static characteristics to improve the starting quality for cars equipped with automated mechanical transmission （AMT） were modeled and simulated. First, axial stiffness of clutch cushion ...The diaphragm spring clutch static characteristics to improve the starting quality for cars equipped with automated mechanical transmission （AMT） were modeled and simulated. First, axial stiffness of clutch cushion spring and characteristic curves of diaphragm spring were theoretically and experimentally studied. Then, model of transfer characteristics of the normal force was built, with special conscen on the abrasion of friction discs and the influence of temperature to diaphragm spring. Finally, the model was tested in practical starting for cars equipped with AMT, which showed that the starting quality was significantly improved. The experimental results showed that the proposed model was precise enough to be implemented conveniently.展开更多
In order to analyze characteristics of Cobot cooperation with a human in a shared workspace, the model of a non-holonormic constraint joint mechanism and its control model were constructed based on double over-running...In order to analyze characteristics of Cobot cooperation with a human in a shared workspace, the model of a non-holonormic constraint joint mechanism and its control model were constructed based on double over-running clutches. The simulation analysis was carried out and it validated passive and constraint features of the joint mechanism. In terms of Cobot components, the control model of Cobot following a desired trajectory was built up. The simulation studies illustrate that the Cobot can track a desired trajectory and possess passive and constraint features ; a human supplies operation force that makes Cobot move, and a computer system con- trois its motion trajectory. So it can meet the requirements of Cobot collaboration with an operator. The Cobot model can be used in applications of material moving, parts assembly and some situations requiring man-machine cooperation and so on.展开更多
The effects of contact surface on dynamic wedging behavior of the roller and inner-ring of the overrunning clutch in a dual-turbine torque converter were investigated to reveal the friction self- locking mechanism and...The effects of contact surface on dynamic wedging behavior of the roller and inner-ring of the overrunning clutch in a dual-turbine torque converter were investigated to reveal the friction self- locking mechanism and dynamic process. Planar strain clutch models including roller, inner-ring and outer-ring were built, and transient wedging process was analyzed with an explicit dynamics meth- od. The modeling of stress and strain distribution and variation of two kinds of contact surfaces show that there are three stages named slipping, wedging and binding respectively during whole wed- ging process. Meanwhile the geometric structures of contact surfaces greatly influence the peak stress and strain distribution of the wedging process of the roller and inner-ring. The load bearing performance of contact surfaces with logarithmic spiral curve is better than that with straight line. Our study provides theoretical foundation for design and further optimization of wedging contact surface of an overrunning clutch in a dual-turbine hydrodynamic torque converter.展开更多
The wet multi-disc clutches are extensively used in various transmission systems,withone of the most prevalent failure modes being the buckling deformation of friction components.Animproved Hilbert-Huang transform met...The wet multi-disc clutches are extensively used in various transmission systems,withone of the most prevalent failure modes being the buckling deformation of friction components.Animproved Hilbert-Huang transform method(IHHT)is proposed to address the limitations of tradi-tional time-domain vibration analyses,such as low accuracy and mode mixing.This paper first clas-sifies the buckling degree of the friction components.Next,wavelet packet transform(WPT)isapplied to the vibration signals of different buckling plates to partition them into distinct fre-quency bands.Then,the instantaneous features are extracted by empirical mode decomposition(EMD)and Hilbert transform(HT)to discarding extraneous intrinsic mode function(IMF)com-ponents.Comparative analyses of Hilbert spectral entropy and time-domain features confirm theenhanced precision of IHHT under specific classifiers,which is better than traditional methods.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
The conventional Continuously Variable Transmission （CVT） has been classified as belt-type or toroidal CVTs. Each CVT is fundamentally composed of several components to transmit the frictional force or torque genera...The conventional Continuously Variable Transmission （CVT） has been classified as belt-type or toroidal CVTs. Each CVT is fundamentally composed of several components to transmit the frictional force or torque generated by the driving force. Since the conventional CVTs use friction force, their energy （force or torque） transfer efficiency might be inferior due to slippage and pressure between the transmission components. Consequently, we propose a new type of structural CVT. The CVT we proposed in this paper means a combined-type transmission with quadric crank chains and one-way clutches.展开更多
According to the statistics, there are about 90 auto clutch assembly and its main parts manufacturers now in China. Before 1985, the main products of these clutch plants were helical spring clutches for truck OE and s...According to the statistics, there are about 90 auto clutch assembly and its main parts manufacturers now in China. Before 1985, the main products of these clutch plants were helical spring clutches for truck OE and service markets. Their production scale was limited and facilities and technological process level were low. Since 1985, Changchun No.228 Factory, Clutch Plant of Nanjing Automobile Works, Shanghai General Plant of Auto展开更多
Numerous hypotheses predict associations between phenotype-associated breeder traits and reproductive success.In secondary cavity-nesting passerine birds,which have been investigated most,up to more than 90parental ch...Numerous hypotheses predict associations between phenotype-associated breeder traits and reproductive success.In secondary cavity-nesting passerine birds,which have been investigated most,up to more than 90parental characteristics have been linked to at least one field measure of breeding performance.However,within study populations,different parental traits,such as clutch size,first-egg date,egg size,nest architecture,plumage colour,adult morphometry,or song performance,are often weakly correlated across female and/or male breeders.Furthermore,many of these studies have been conducted outside the theoretical framework of the'Individual Optimisation Hypothesis' of clutch size(IOH).IOH predicts that:(i) females with larger clutches will have larger broods at hatching and fledging compared to those with smaller clutches;and(ii) clutch size,which is adaptively adjusted to the parents' ability to rear nestlings,should always maximize the percentage of eggs producing fledglings so that variation in clutch size becomes disconnected from variation in breeding success.In this paper,we present the first detailed review of implications of IOH for parental characters other than clutch size.Our review covered 188 non-experimental studies and 1074 statistical results that examined how parental traits influence breeding success in Western Palearctic Great Tits(Parus major),Blue Tits(Cyanistes spp.),and flycatchers(Ficedula spp.).Clutch size explained one third of the variation in brood size at hatching and fledging within study populations.However,most parental characteristics associated weakly with the number of hatchlings or fledglings,likely because they did not correlate with clutch size.Overall,parental traits were poorly correlated with the proportion of hatchlings and fledglings per egg.We discuss why intraspecific variation in phenotype-associated breeder traits is often disconnected from interindividual differences in breeding success,and highlight the importance of underexplored research problems in avian breeding biology.展开更多
Armored vehicles,to accomplish missions in complex harsh conditions with high mobility,require the transmission system to achieve high energy density and high reliability.The wet multi-disc clutch becomes the perishab...Armored vehicles,to accomplish missions in complex harsh conditions with high mobility,require the transmission system to achieve high energy density and high reliability.The wet multi-disc clutch becomes the perishable component under heavy load,large speed difference,and frequent engagement.Due to the difficulty of maintenance in battlefield,clutch carrying post-buckling separate plate is common,and the clutch working process is obstructed.Therefore,considering the post-buckling plate,the multi-physics thermodynamic model of a wet multi-disc clutch is established to describe the entire engagement and separation process.The influence of the buckling degree on the stress-strain,uniformity of gaps,torque,and temperature characteristics is investigated by the numerical method and testified by bench tests.The results show that with the increasing buckling degree,the clutch engagement and separation times decrease gradually.For the separation process,the non-uniformity of gaps is increased,and gaps are eventually occupied,leading to the continuous rough contact among friction pairs.Therefore,the drag torque is increased.Squeezed by the post-buckling plate,the cooling rates of separate plates are decreased.During repeated engagement-separation,temperatures of plates may reach balance points.Since continuous sliding and temperature concentration,the wear form and degree changes,especially at outer radius.Extra drag torque,heat,and wear threats the friction components which increases the risk of failures of the transmission system and affects the mobility of armored vehicles.展开更多
This study aims to develop an accurate calculation model of transmission torque and load-bearing capacity for hydro-viscous clutches(HVC)used in high-power vehicles,which is important to investigate the step-less spee...This study aims to develop an accurate calculation model of transmission torque and load-bearing capacity for hydro-viscous clutches(HVC)used in high-power vehicles,which is important to investigate the step-less speed regulation characteristics in a fan drive system.However,most of the existing models ignore the distribution differences of groove area along the radial direction,which may lead to significant deviations in calculating the mechanical property of friction pairs related to operating conditions and the engagement process.To fill this gap,a new calculation model for bearing capacity and frictional torque of friction pairs with different oil grooves is proposed,in which the traditional fixed contact area ratio coefficient for oil groove measurement is replaced by a more precise discrete micro-ring area ratio(DMAR)integration method.Then,a 32-degree-of-freedoms dynamic model of HVC at a fan drive system is established for the prediction of dynamic responses during speed regulation.Results show that friction pairs with different oil grooves have a direct influence on frictional torque and bearing capacity through the change of DMAR along the radial direction.The friction pairs with different groove structures have oscillation phenomena at the engagement steady-state boundary.Furthermore,a step-less speed regulation experimental setup is established to verify the correctness of the proposed model.It is demonstrated that the axial engagement force and the speed regulation curve predicted by the proposed method are in good agreement with the experimental data.The results could effectively predict the engagement dynamic characteristics.The numerical relationship among the structure parameters,the mechanical properties of friction pairs,and the speed regulation characteristics of the system are established through the proposed model,which lays a theoretical foundation for the structure design of friction plates and optimization of step-less speed regulation performance.展开更多
The control of the clutch engagement for an automatic mechanical transmission in the process of a tracklayer getting to start is studied. The dynamic model of power transmission and automatic clutch system is develope...The control of the clutch engagement for an automatic mechanical transmission in the process of a tracklayer getting to start is studied. The dynamic model of power transmission and automatic clutch system is developed. Using tools of Simulink, the transient characteristics during the vehicle starting, including the jerk and the clutch slip time, are provided here. Based on the analyses of the simulation results and driver’s experiences, a fuzzy controller is designed to control the clutch engagement. Simulation results verify its value.展开更多
Based on the theoretical analyses, the dynamic and mathematical models of the system were developed. The models were implemented in the ambit of the Matlab/Simulink environment, and an integrated simulation model was ...Based on the theoretical analyses, the dynamic and mathematical models of the system were developed. The models were implemented in the ambit of the Matlab/Simulink environment, and an integrated simulation model was developed. The dynamic performance of the power shift clutch during engagement and disengagement was studied by using this assembly model. The sliding speed, torque transmitted through the clutch, and the rate at which energy is dissipated during the process were determined. Using this model, the calculation during simulation can be simplified. This lays a foundation for the dynamic performance research on the power train with the power shift clutch, and provides a powerful tool for developing an automatic, electronically controlled transmission.展开更多
The oil film clutch, which is superior in speed adjustment, is capable of being used in the belt conveyor to carry out soft start operation. According to running properties of both belt conveyor and oil film clutch...The oil film clutch, which is superior in speed adjustment, is capable of being used in the belt conveyor to carry out soft start operation. According to running properties of both belt conveyor and oil film clutch, equations that are used to decide the lubricating oil flow and the number of oil films (i.e. the number of rotating and stationary plates) are deduced theoretically. Also key parameters are provided for the design of the hydraulic system. All these together provide the theoretical basis for the soft start design of the belt conveyor and references for the application of the oil film clutch in similar fields.展开更多
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
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The presented results are based on the research project FVA no.343/Ⅲ undertaken by the Research Association for Drive Technology e.V.(FVA).
文摘Wet multi-plate clutches are relevant components of modern drivetrain applications,not only in terms of function but also safety and comfort.Especially at the beginning of their lifetime,distinct changes of the friction behavior may occur and make the actuation of the clutch challenging.This transcript describes the typical running-in behavior of wet multi-plate clutches and gives a general definition for running-in of clutches.Moreover,a new test method to systematically investigate the running-in behavior of clutches is introduced.This test method contains a test procedure to characterize the running-in behavior on different load levels.Furthermore,a multi-stage procedure to evaluate and characterize the running-in behavior of clutches with mathematical approaches and new characteristic values is given.The quality of the test method is demonstrated on the example of three different tribological systems from dual clutch transmissions(DCT)and automatic transmissions(AT)application using paper friction linings.
基金the National Natural Science Foundation of China(No.51475284)
文摘A force-aided lever with a preload spring is not only force-saving but also energy-saving. Therefore, it has great potential to be applied to dry clutch actuations. However, the negative stiffness of the clutch diaphragm spring introduces unstable dynamics which becomes more intensive due to the preload spring. In order to explore the intensified unstability, this paper builds dynamic models for the rotating lever coupling a negative stiffness diaphragm spring and a preload spring. The stability analysis using the Routh-Huiwitz criterion shows that the open-loop system can never be stable due to the negative stiffness. Even if the diaphragm spring stiffness is positive, the system is still unstable when the preload of the spring exceeds an upper limit. A proportionalintegral-derivative(PID) closed-loop scheme addressing this problem is designed to stabilize the system. The stability analysis for the closed-loop system shows that stable region emerges in spite of the negative stiffness; the more the negative stiffness is, the less the allowed preload is. Further, the influences of the dimensions and PID parameters on the stability condition are investigated. Finally, the transient dynamic responses of the system subjected to disturbance are compared between the unstable open-loop and stabilized closed-loop systems.
基金National Natural Science Foun-dation of China(Grant No.32170481 and Grant No.3221153042).
文摘The brain is among the most energetically costly organs in vertebrates,and thus trade-offs have been hypothesized to exert constraints on brain size evolution.The energy trade-off hypothesis(ETH) predicts that reducing the energy consumption of reproduction or other costly tissues should compensate for the cost of a large brain.Egg production in birds requires a large proportion of the total energy budget,and a clutch mass in some bird species can outweigh the body mass of the female.To date,this hypothesis has mainly been tested in mammals and ectothermic animals such as anurans and fishes.We collated data on adult brain size,body mass and eggproduction traits such as clutch size,egg mass and annual broods from published studies,and conducted a phylogenetic comparative test of the interplay between egg-production investment and brain size evolution across bird species.After controlling for phylogenetic relationships and body size,we find a negative correlation between brain size and clutch size across 1395 species,which favored ETH.However,when egg mass was integrated in models,positive associations were detected between brain size and mass of eggs(via egg mass,clutch mass and annual total egg mass).Our results suggest that brain size trades off against egg-production only via certain aspects(e.g.,clutch size).By contrast,a positive relationship between brain size and total egg reproduction(e.g.,clutch mass and annual total egg mass) implied increased total energy budget outweighing energy allocation across bird species.Our study shows that there is no general energy trade-off between brain size and eggreproduction investment,and suggests that brain size evolution follows mixed strategies across bird species.
基金Supported by the National Natural Science Foundation of China(51275038)
文摘The diaphragm spring clutch static characteristics to improve the starting quality for cars equipped with automated mechanical transmission （AMT） were modeled and simulated. First, axial stiffness of clutch cushion spring and characteristic curves of diaphragm spring were theoretically and experimentally studied. Then, model of transfer characteristics of the normal force was built, with special conscen on the abrasion of friction discs and the influence of temperature to diaphragm spring. Finally, the model was tested in practical starting for cars equipped with AMT, which showed that the starting quality was significantly improved. The experimental results showed that the proposed model was precise enough to be implemented conveniently.
基金Sponsored by the National Natural Science Foundation of China(Grant No60275030)
文摘In order to analyze characteristics of Cobot cooperation with a human in a shared workspace, the model of a non-holonormic constraint joint mechanism and its control model were constructed based on double over-running clutches. The simulation analysis was carried out and it validated passive and constraint features of the joint mechanism. In terms of Cobot components, the control model of Cobot following a desired trajectory was built up. The simulation studies illustrate that the Cobot can track a desired trajectory and possess passive and constraint features ; a human supplies operation force that makes Cobot move, and a computer system con- trois its motion trajectory. So it can meet the requirements of Cobot collaboration with an operator. The Cobot model can be used in applications of material moving, parts assembly and some situations requiring man-machine cooperation and so on.
基金Supported by the National Natural Science Foundation of China(51475041)the Ministerial Level Advanced Research Foundation(40402060103)the Ministerial Basic Products Innovation Program(VTDP2104)
文摘The effects of contact surface on dynamic wedging behavior of the roller and inner-ring of the overrunning clutch in a dual-turbine torque converter were investigated to reveal the friction self- locking mechanism and dynamic process. Planar strain clutch models including roller, inner-ring and outer-ring were built, and transient wedging process was analyzed with an explicit dynamics meth- od. The modeling of stress and strain distribution and variation of two kinds of contact surfaces show that there are three stages named slipping, wedging and binding respectively during whole wed- ging process. Meanwhile the geometric structures of contact surfaces greatly influence the peak stress and strain distribution of the wedging process of the roller and inner-ring. The load bearing performance of contact surfaces with logarithmic spiral curve is better than that with straight line. Our study provides theoretical foundation for design and further optimization of wedging contact surface of an overrunning clutch in a dual-turbine hydrodynamic torque converter.
文摘The wet multi-disc clutches are extensively used in various transmission systems,withone of the most prevalent failure modes being the buckling deformation of friction components.Animproved Hilbert-Huang transform method(IHHT)is proposed to address the limitations of tradi-tional time-domain vibration analyses,such as low accuracy and mode mixing.This paper first clas-sifies the buckling degree of the friction components.Next,wavelet packet transform(WPT)isapplied to the vibration signals of different buckling plates to partition them into distinct fre-quency bands.Then,the instantaneous features are extracted by empirical mode decomposition(EMD)and Hilbert transform(HT)to discarding extraneous intrinsic mode function(IMF)com-ponents.Comparative analyses of Hilbert spectral entropy and time-domain features confirm theenhanced precision of IHHT under specific classifiers,which is better than traditional methods.
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.
文摘The conventional Continuously Variable Transmission （CVT） has been classified as belt-type or toroidal CVTs. Each CVT is fundamentally composed of several components to transmit the frictional force or torque generated by the driving force. Since the conventional CVTs use friction force, their energy （force or torque） transfer efficiency might be inferior due to slippage and pressure between the transmission components. Consequently, we propose a new type of structural CVT. The CVT we proposed in this paper means a combined-type transmission with quadric crank chains and one-way clutches.
文摘According to the statistics, there are about 90 auto clutch assembly and its main parts manufacturers now in China. Before 1985, the main products of these clutch plants were helical spring clutches for truck OE and service markets. Their production scale was limited and facilities and technological process level were low. Since 1985, Changchun No.228 Factory, Clutch Plant of Nanjing Automobile Works, Shanghai General Plant of Auto
文摘Numerous hypotheses predict associations between phenotype-associated breeder traits and reproductive success.In secondary cavity-nesting passerine birds,which have been investigated most,up to more than 90parental characteristics have been linked to at least one field measure of breeding performance.However,within study populations,different parental traits,such as clutch size,first-egg date,egg size,nest architecture,plumage colour,adult morphometry,or song performance,are often weakly correlated across female and/or male breeders.Furthermore,many of these studies have been conducted outside the theoretical framework of the'Individual Optimisation Hypothesis' of clutch size(IOH).IOH predicts that:(i) females with larger clutches will have larger broods at hatching and fledging compared to those with smaller clutches;and(ii) clutch size,which is adaptively adjusted to the parents' ability to rear nestlings,should always maximize the percentage of eggs producing fledglings so that variation in clutch size becomes disconnected from variation in breeding success.In this paper,we present the first detailed review of implications of IOH for parental characters other than clutch size.Our review covered 188 non-experimental studies and 1074 statistical results that examined how parental traits influence breeding success in Western Palearctic Great Tits(Parus major),Blue Tits(Cyanistes spp.),and flycatchers(Ficedula spp.).Clutch size explained one third of the variation in brood size at hatching and fledging within study populations.However,most parental characteristics associated weakly with the number of hatchlings or fledglings,likely because they did not correlate with clutch size.Overall,parental traits were poorly correlated with the proportion of hatchlings and fledglings per egg.We discuss why intraspecific variation in phenotype-associated breeder traits is often disconnected from interindividual differences in breeding success,and highlight the importance of underexplored research problems in avian breeding biology.
基金supported by the National Natural Science Foundations of China(Grant Nos.52205047,52175037)Frontier Cross Project of Beijing Institute of Technology(Grant No.2024CX11006)。
文摘Armored vehicles,to accomplish missions in complex harsh conditions with high mobility,require the transmission system to achieve high energy density and high reliability.The wet multi-disc clutch becomes the perishable component under heavy load,large speed difference,and frequent engagement.Due to the difficulty of maintenance in battlefield,clutch carrying post-buckling separate plate is common,and the clutch working process is obstructed.Therefore,considering the post-buckling plate,the multi-physics thermodynamic model of a wet multi-disc clutch is established to describe the entire engagement and separation process.The influence of the buckling degree on the stress-strain,uniformity of gaps,torque,and temperature characteristics is investigated by the numerical method and testified by bench tests.The results show that with the increasing buckling degree,the clutch engagement and separation times decrease gradually.For the separation process,the non-uniformity of gaps is increased,and gaps are eventually occupied,leading to the continuous rough contact among friction pairs.Therefore,the drag torque is increased.Squeezed by the post-buckling plate,the cooling rates of separate plates are decreased.During repeated engagement-separation,temperatures of plates may reach balance points.Since continuous sliding and temperature concentration,the wear form and degree changes,especially at outer radius.Extra drag torque,heat,and wear threats the friction components which increases the risk of failures of the transmission system and affects the mobility of armored vehicles.
基金Supported by the National Natural Science Foundation of China(Grant Nos.52475089,52035002)National Key Research and Development Program of China(Grant No.2021YFB2011400)the Chongqing Natural Science Foundation(Grant No.CSTB2022NSCQ-MSX1243).
文摘This study aims to develop an accurate calculation model of transmission torque and load-bearing capacity for hydro-viscous clutches(HVC)used in high-power vehicles,which is important to investigate the step-less speed regulation characteristics in a fan drive system.However,most of the existing models ignore the distribution differences of groove area along the radial direction,which may lead to significant deviations in calculating the mechanical property of friction pairs related to operating conditions and the engagement process.To fill this gap,a new calculation model for bearing capacity and frictional torque of friction pairs with different oil grooves is proposed,in which the traditional fixed contact area ratio coefficient for oil groove measurement is replaced by a more precise discrete micro-ring area ratio(DMAR)integration method.Then,a 32-degree-of-freedoms dynamic model of HVC at a fan drive system is established for the prediction of dynamic responses during speed regulation.Results show that friction pairs with different oil grooves have a direct influence on frictional torque and bearing capacity through the change of DMAR along the radial direction.The friction pairs with different groove structures have oscillation phenomena at the engagement steady-state boundary.Furthermore,a step-less speed regulation experimental setup is established to verify the correctness of the proposed model.It is demonstrated that the axial engagement force and the speed regulation curve predicted by the proposed method are in good agreement with the experimental data.The results could effectively predict the engagement dynamic characteristics.The numerical relationship among the structure parameters,the mechanical properties of friction pairs,and the speed regulation characteristics of the system are established through the proposed model,which lays a theoretical foundation for the structure design of friction plates and optimization of step-less speed regulation performance.
文摘The control of the clutch engagement for an automatic mechanical transmission in the process of a tracklayer getting to start is studied. The dynamic model of power transmission and automatic clutch system is developed. Using tools of Simulink, the transient characteristics during the vehicle starting, including the jerk and the clutch slip time, are provided here. Based on the analyses of the simulation results and driver’s experiences, a fuzzy controller is designed to control the clutch engagement. Simulation results verify its value.
文摘Based on the theoretical analyses, the dynamic and mathematical models of the system were developed. The models were implemented in the ambit of the Matlab/Simulink environment, and an integrated simulation model was developed. The dynamic performance of the power shift clutch during engagement and disengagement was studied by using this assembly model. The sliding speed, torque transmitted through the clutch, and the rate at which energy is dissipated during the process were determined. Using this model, the calculation during simulation can be simplified. This lays a foundation for the dynamic performance research on the power train with the power shift clutch, and provides a powerful tool for developing an automatic, electronically controlled transmission.
文摘The oil film clutch, which is superior in speed adjustment, is capable of being used in the belt conveyor to carry out soft start operation. According to running properties of both belt conveyor and oil film clutch, equations that are used to decide the lubricating oil flow and the number of oil films (i.e. the number of rotating and stationary plates) are deduced theoretically. Also key parameters are provided for the design of the hydraulic system. All these together provide the theoretical basis for the soft start design of the belt conveyor and references for the application of the oil film clutch in similar fields.
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.
