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The relationship between clutch thermodynamic characteristics and contact states of friction components is explored numerically and experimentally. The clutch thermodynamic numerical model is developed with consideration of the contact state and oil film between friction pairs. The clutch bench test is conducted to verify the variation of the clutch thermodynamic characteristics from the uniform contact (UCS) to the intermittent contact (ICS). The results show that the oil film decreases gradually with increasing temperature; the lubrication state finally changes from hydrodynamic lubrication to dry friction, where the friction coefficient shows an increasing trend before a decrease. Thus, the friction torque in UCS gradually increases after the applied pressure stabilizes. When the contact state changes to ICS, the contact pressure increases suddenly and the oil film decreases rapidly in the local contact area, bringing about a sharp increase in friction torque; subsequently, the circumferential and radial temperature differences of friction components expand dramatically. However, if the contact zone is already in the dry friction state, friction torque declines directly, resulting in clutch failure. The conclusions can potentially be used for online monitoring and fault diagnosis of the clutch. [ABSTRACT FROM AUTHOR]

Failures of multi-plate clutches must be reliably excluded due to safety-critical functionalities in the drive train. The main reason for failures of multi-plate clutches due to long-term and spontaneous damage is thermal damage. In this paper, a parameterizable two-dimensional finite element model is developed and validated for damage prevention and for analyzing the thermo-mechanical behavior of a clutch in transient operation. Both numerical verification and validation with experimental results are very good despite the simplifications in the model. Subsequently, the temperature and pressure distribution of the individual friction areas is determined. The results show that the maximum temperatures tend to occur at the outer diameter of the friction area. The pressure distribution is very homogeneous. In a parameter study, the influence of Young's modulus of the friction lining, the thermal conductivity of the friction lining, and the steel plate thickness on the temperature and pressure behavior in the clutch is investigated. Although the Young's modulus of the friction lining influences the pressure distribution in the friction contact, the temperature behavior is only slightly changed by the variation of the elastic modulus due to the load case. The thermal conductivity of the lining and steel plate thickness have a strong influence on the temperature level in the clutch. However, the distribution of pressures is still very homogeneous compared to the reference model. [ABSTRACT FROM AUTHOR]

Failures of multi-plate clutches must be reliably excluded due to safety-critical functionalities in the drive train. The main reason for failures of multi-plate clutches due to long-term and spontaneous damage is thermal damage. In this paper, a parameterizable two-dimensional finite element model is developed and validated for damage prevention and for analyzing the thermo-mechanical behavior of a clutch in transient operation. Both numerical verification and validation with experimental results are very good despite the simplifications in the model. Subsequently, the temperature and pressure distribution of the individual friction areas is determined. The results show that the maximum temperatures tend to occur at the outer diameter of the friction area. The pressure distribution is very homogeneous. In a parameter study, the influence of Young’s modulus of the friction lining, the thermal conductivity of the friction lining, and the steel plate thickness on the temperature and pressure behavior in the clutch is investigated. Although the Young’s modulus of the friction lining influences the pressure distribution in the friction contact, the temperature behavior is only slightly changed by the variation of the elastic modulus due to the load case. The thermal conductivity of the lining and steel plate thickness have a strong influence on the temperature level in the clutch. However, the distribution of pressures is still very homogeneous compared to the reference model.

This paper presents an investigation of the hot judder behavior in a multi-disc clutch with the uneven contact pressure and the initial temperature taken into account. Considering the actual structure of clutch, the pressure function is achieved to describe the uneven contact pressure distribution due to the circlip constraint. Moreover, the pin-on-disc test is conducted to obtain the formula of the coefficient of friction with the contact pressure, surface temperature, and rotating speed involved. The thermal and dynamic models are established and coupled to evaluate the hot judder behavior. The results demonstrate that the uneven contact pressure has a slight influence on the clutch hot judder, but it expands the radial temperature difference on the friction surface; meanwhile, the friction torque generated on the friction surface closer to the circlip is larger. Although the increase of initial temperature can shorten the clutch engagement time, the clutch hot judder will be shriller, as verified in the SAE#2 bench test. Furthermore, in order to reduce the clutch hot judder, the circlip should be optimized to smooth the radial contact pressure, and the advanced thermal management method should be applied to strengthen the clutch heat dissipation. [ABSTRACT FROM AUTHOR]

The heat partition coefficient between two finite thickness contact discs during long-time sliding is studied with a coupled finite element method. Results show that the heat partition coefficient varies from its initial value to another steady state value rapidly instead of being a constant all the time. An analytical solution of the temperature field under invariant heat flux input is deduced, which tells that there exists a unique critical thickness ratio between the contact discs that keeps the heat partition coefficient a constant. An equivalent method for single-material contact bodies is proposed that is capable of calculating the steady state heat partition coefficient for any thickness ratio. It reveals that the steady state heat partition coefficient only has relationship with the mass density and the heat capacity of the materials and the thickness ratio. Based on this method, a two-step material equivalent method is further proposed for the contact discs that have friction linings on them. The solution shows that the steady state heat partition coefficient in this situation is also only determined by the material properties and the layer thicknesses. A test bench of multi-disc clutch is set up and a series of sliding experiments are conducted to validate the proposed equivalent methods and solutions of steady state heat partition coefficient. The measured experimental temperature variations show that the temperature level of the separator disc in the clutch is overestimated with the constant heat partition coefficient of semi-infinite model, while it is close to those calculated results with steady state heat partition coefficient. Therefore, the temperature fields of the contact discs during long-time sliding with constant speed can be figured out efficiently using the steady state heat partition coefficient with only small error, and these equivalent methods benefit the multi-disc clutch design and temperature estimation in practical applications. [ABSTRACT FROM AUTHOR]

The comprehensive fault diagnosis method has been developed to analyze the failure of the multi-disc clutch. The mechanical buckling model is developed to investigate the relationship between the resistance torque and the periodic circumferential bright spots. The contact pressure and temperature on the friction surfaces are obtained with the consideration of the concentrated reactive load of the circlip. The friction and wear characteristics of the friction disc under different temperature conditions are explored by the pin-on-disc test, and then the surface morphologies of tested discs are observed by the metalloscope. The results demonstrate that both the thermal buckling and the mechanical buckling can result in the mechanical-thermal buckling. As the temperature varies from 15 °C to 400 °C, the disc experiences the abrasive wear, ploughing wear, adhesive wear and delamination wear in order. Finally, the mechanical-thermal safety boundaries are proposed. Moreover, the paper provides some suggestions for better design of clutch: the circlip should be optimized to avoid stress concentration; the teeth number of separate plates should be increased to improve the torque transmission capacity; the thickness of separate plates should be different which can be determined by their axial positions in the clutch pack. • The model for circumferential mechanical buckling is presented and validated. • The comprehensive fault diagnosis method of the multi-disc clutch is developed. • The effect of temperature on the friction and wear characteristics of a disc is studied. • The safety mechanical-thermal boundary of the clutch is proposed and validated. • The thickness of separate plate should be varied according to its axial position. [ABSTRACT FROM AUTHOR]

A full-scale multi-disc clutch test bench was set up and some sliding experiments were conducted to investigate the temperature evolution processes in low and high lubrication regimes. Friction discs with single friction lining were used and arranged back-to-back in order to preserve possible evidences of buckling. Temperatures were measured with thermocouples from four different radii on the mid-plane of the separator disc. Two different kinds of temperature variation processes with obvious critical points of cone shape buckling were obtained. These temperatures can be divided into three effective stages that represent different deformation status of the discs in these experiments. The temperature fields in the contacting separator disc and friction disc were studied through a transient heat conduction model, and the results show that the temperatures measured by the thermocouples from the separator disc can represent the average temperatures in both of the separator disc and friction disc for a long sliding time. By comparing the computational critical moments of the friction components with the experimental results, the capability of the curved beam model for predicting the critical moments of cone buckling was validated. [ABSTRACT FROM PUBLISHER]

Lubricated friction systems and their friction materials have to fulfil high standards concerning mechanical and thermal load capacity, wear, and coefficient of friction. Engineering ceramics show high potential to increase the power density of these systems.To realize the potential of new materials, it is necessary to provide suitable methods and tools to design high loaded lubricated friction systems with increased performance. Representative for high-loaded friction systems with low pressure and high sliding speed, a lubricated multi-disc clutch has been chosen as a demonstrator system. This demonstrator system is being used to deepen knowledge about the tribological system's behaviour. [ABSTRACT FROM AUTHOR]

As an essential part of the transmission, the life of the clutch directly affects the stability of the transmission. In this paper, a finite element model and a thermodynamic numerical model of a multi-disc clutch are established to investigate the influence of material parameters on the contact pressure distribution. The pressure distribution index (PDI) is firstly proposed to evaluate the pressure difference among friction pairs. Moreover, the correctness of the numerical model is verified by the clutch static pressure experiment. The results show that increasing the elastic modulus and Poisson's ratio of the backplate can effectively improve the uniformity of the contact pressure. However, the variations in material parameters of other clutch components can not easily smooth the pressure difference. Therefore, optimized material parameters for the clutch are proposed, where the maximum pressure and temperature differences are reduced by about 27.2% and 10.3%, respectively. [ABSTRACT FROM AUTHOR]

• The plate thermodynamic differences before and after deformation are presented. • The friction torque and temperature of plate increase suddenly in the deformation. • The critical circumferential temperature gradient for the deformation is 2–3 °C. This work is devoted to investigate the thermodynamic characteristics of the deformed separate plate in a multi-disc clutch. The thermodynamic model is proposed, and the contact ratio of mating surface is varied to imitate the deformed plate. Moreover, the experimental study is conducted on the clutch test bench; in order to induce the plate deformation more easily, the thermometric plate has experienced the circumferential elastic deformation before experiments. Before the elastic deformation of separate plate occurs, the surface temperature increases steadily and the friction torque increases slowly with the increase of coefficient of friction. When the temperature gradient in the circumferential direction reaches the critical value 2–3 °C, the elastic deformation is excited. In the process of elastic deformation, the temperature growth rate in the contact zone increases dramatically, and the friction torque rises steeply. As for the variation of friction torque after the elastic deformation, it can be divided into three categories: increase smoothly, stable and decrease gradually. Moreover, at this stage, the smaller the contact ratio is, the higher the temperature in the contact zone is, and the greater the friction torque is. Meanwhile, with the decrease of the radial length and circumferential angle in the contact zone, the radial and circumferential temperature differences of the plate expand dramatically. The conclusions can be used as a theoretical basis for evaluating the real-time status of friction components and diagnosing the clutch failure. [ABSTRACT FROM AUTHOR]