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A fundamental understanding of wet clutches' drag loss behavior is essential for designing efficient clutch systems. It has been widely recognized that the separation behavior immediately after disengaging the clutch and the resulting clearance distribution influence the drag loss behavior. However, these influencing factors have yet to be systematically investigated. Therefore, this study aimed to experimentally investigate the effects of plate separation and clearance distribution on drag loss behavior under different operating conditions and modes. For this purpose, image series of an operating clutch system were recorded and subsequently analyzed using image processing algorithms to evaluate the movements of the plates. Based on this, the effects on drag loss behavior were analyzed. The investigations were carried out on a clutch system used in an industrial application. The measurements show that the axial movements of the plates comprise main and superimposed non-periodic movements of much a smaller amplitude. The separation of the plates is primarily driven by the applied differential speed so that the set total clearance is only utilized mainly in the higher differential speed range. The separation behavior, therefore, decisively influences the drag loss behavior. The plates can even remain in contact in the low differential speed range. The investigations also showed that the separation behavior and, thus, the drag loss behavior can be improved by using waved plates, especially in the low differential speed range. It was also found that a high plate number and a large set total clearance support a non-uniform clearance distribution. Based on the investigations conducted, it is possible to expand our fundamental knowledge of separation behavior and clearance distribution, allowing for a reduction in the drag losses of wet clutches. The findings can thus contribute to the development of low-loss and compact clutch systems. [ABSTRACT FROM AUTHOR]

High-speed electric drive units promise improved power density and, theoretically, driving range of battery electric vehicles. An essential step of the development process is extensive testing of the drive unit on a test rig. In particular, at a high rotational speed level, experimental testing can be challenging. This paper describes a test rig for investigating the overall function of a high-speed drive unit and the transmission's efficiency and dynamics. The high-speed drive unit developed in the Speed4E research project was the reference drive unit. The test rig is based on the concept of electrical power circulation. Thus, the test rig can be used universally for different drive unit designs and operating modes. A reaction torque measurement unit was developed to enable measurements at high rotational speeds. Simultaneously, this unit allows robust measurements at low costs. The expected measurement uncertainties of torque, rotational speed, transmission efficiency, and power losses were calculated using the Monte Carlo method. The results demonstrate that the developed torque measurement unit combines precise torque measurement with a robust design and low costs, making it competitive with state-of-the-art solutions for torque measurement at high speeds. [ABSTRACT FROM AUTHOR]

The safe and efficient torque transmission of wet disk clutch systems requires high coefficients of friction. To achieve good controllability and high comfort, a positive slope of the coefficient of friction over sliding velocity is ensured by a reasonable formulation of the lubricant and choice of the friction pairing. This results in low transmittable torque at low sliding velocities. Thus, the occurrence of unwanted micro-slip in dynamic operation modes must be considered for the design of safety-relevant clutch systems. This work presents a methodology for the holistic measurement of the friction behavior of wet disk clutches. It is suitable for numerous applications and supports a sound understanding of frictional properties in the range of sliding velocities occurring in brake shifts through forced slip operation down to static torque transmission. The experimental determination of the holistic friction behavior is crucial for developing optimized design guidelines for modern clutch systems. [ABSTRACT FROM AUTHOR]

Fundamental knowledge of wet clutches’ drag loss behavior is essential for designing low-loss clutch systems. In contrast to the widely investigated injection lubrication, more comprehensive knowledge is needed on the drag loss behavior of dip-lubricated wet clutches. In the development phase, data-driven models allow drag loss predictions with low computational effort and, at the same time, sufficient accuracy. Therefore, this study aimed to deepen and expand knowledge of the drag loss behavior of dip-lubricated wet clutches based on experimental investigations. Moreover, the investigations were designed and conducted so that the generated data and findings can be used in further research for building data-driven prediction models. The investigations were conducted on two clutch systems from automotive and industrial applications. The practice-relevant parameters of clearance, oil level, oil viscosity, and plate shape were investigated based on a mixed-level full factorial design. The evaluation shows that a reduction in drag loss can be achieved primarily by increasing the clearance, reducing the oil viscosity, and choosing waved plates. The obtained drag loss behavior can be traced back to the form of oil displacement from the gaps. The displacement process, in turn, is influenced by the operating and geometry parameters. Although the flow in the gaps develops differently for dip and injection lubrication over differential speed, the study shows comparable integral effects of the influencing parameters for both types of lubrication. The generated datasets contain the investigated parameters as features and characteristic drag loss values as targets. The findings can support the selection and configuration of the machine learning algorithm and the validation of the trained models. The described procedure can serve as a template for generating and analyzing datasets for data-driven modeling of wet clutches’ drag losses. [ABSTRACT FROM AUTHOR]

In the design of rear-axle locking differentials, the desired high locking effect is often achieved using wet multi-plate clutches. This study conducts an in-depth investigation into the spontaneous damage behavior of these clutches through a series of methodical experimental tests. It focuses on three different clutch variants, each equipped with organic friction linings—namely, paper-based, carbon composite, and woven carbon—and undertakes a comparative analysis of their respective damage typologies. The experimental analysis identifies and characterizes patterns of damage, notably the buckling of steel plates and the detachment of lining. Moreover, the study thoroughly examines and compares the friction and temperature behavior under the high load conditions applied to these three friction systems. Concurrent temperature measurements enable the establishment of robust temperature-based criteria for predicting and understanding damage behavior. [ABSTRACT FROM AUTHOR]

The driving comfort and safety of the automotive powertrain are significantly related to the performance, lifetime, and functionality of the lubricant. The presented study focuses on investigating the performance loss of the lubricant due to water contamination resulting from environmental influences and iron particles originating from the wear of different machine elements. The main purpose is to determine critical factors that contribute to the degradation of the lubricant, and increase the tendency to NVH behavior, leading to adverse comfort losses to the respective user. Therefore, this performance loss is evaluated by test rig-based analysis of the friction behavior of wet clutches. Due to physical adsorption, a significant impact of water and iron contamination on the degradation of the lubricant is found, while the influence of the energy input is secondary. [ABSTRACT FROM AUTHOR]

For wet disk clutches, the energy input is strongly influenced by its friction behavior. However, the friction behavior cannot be simulated and therefore is mostly derived from experimental data for specific clutch systems. This paper presents a new approach for the identification and validation of linear friction models using analysis of variance (ANOVA) and stepwise regression. Therefore, we use experimental data of three different friction systems with paper- and carbon-based friction lining. The designed experiments support an efficient parameter-based analysis of the friction behavior. The obtained models can be used as an input for thermal simulations, for example, but can also support a better understanding of the main influencing factors and are applicable to various friction systems. For validation, the obtained models are applied to measured data. A good correspondence between the simulated and measured friction behavior can be shown for speeds in the investigated operating range. The presented procedure can be easily adapted, for different factors and operation modes, as well as other applications. [ABSTRACT FROM AUTHOR]

Carbon friction linings are increasingly being used for clutches in industrial applications because of their excellent properties in terms of friction behavior, temperature resistance, and wear. Due to safety-relevant use of these clutches, their failure must be avoided and thus the damage behavior must be investigated. In this article, the spontaneous damage behavior of two multi-plate clutches (FS1, FS2) with different carbon friction linings (a woven and a composite carbon friction lining) is investigated experimentally. For this purpose, the mechanical load was increased step by step in step tests with brake shifting and the damage progression was documented by regular dismounting of the clutch. For the FS1 friction system with a composite carbon friction lining, the initial damage was local discoloration of the steel plates due to oil cracking products. The failure of the system occurred in friction system 1 due to shrinkage of the steel plates on the inner carrier. For the FS2 friction system with a woven carbon friction lining, the initial damage was also discoloration of the steel plate. With increasing load there was displacement of the friction lining pads. The failure of the system was caused by the detachment of the friction lining from the carrier plate. The research results highlight the potential for improvement of the multi-plate clutch in terms of a more temperature-resistant adhesive layer between the carrier plate and the friction lining. In addition, the steel plates must be heated evenly in the radial direction, which can be achieved by optimizing the geometry. [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]

Wet multi-plate clutches enable safety-critical operations in various types of powertrains. Ensuring sufficient oil coverage on each friction interface of industrial clutches is achieved by pressurized oil supply. The challenge of building capable test rigs to study oil and pressure distribution inside a practically relevant loaded clutch and the limited availability of test parts due to small batch sizes determine the demand for numerical studies. This contribution presents results obtained by experimentation on a component test rig and by numerical studies with computational fluid mechanics of a wet industrial clutch. A transient moving mesh approach with a laminar, incompressible, and isothermal flow model is applied to the fluid domain representing the test rig setup. The investigations are validated by comparing pressure measurements with simulation results. The influences of varying operating conditions (oil flow, speed) and geometry of oil supply in the inner carrier on the oil and pressure distributions are analyzed. Regardless of operating conditions or geometrical variations of the inner carrier, a nearly uniform oil supply to all friction interfaces is achieved. The hydraulic oil pressure lowers the effective axial force at the friction interfaces, and therefore reduces torque transfer capacity up to 29%, depending on operating conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Wet-running multi-plate clutches should be prevented from failing due to the often safety-relevant functions they fulfill in the drive train. In addition to long-term damage, spontaneous damage is of particular relevance for failures. This paper focuses on the influence of spontaneous damage on frictional behavior in the later life cycle. The aim of the experimental investigations is to initially cause spontaneous damage in wet-running multi-plate clutches with sintered friction linings. For this purpose, three clutches are first pre-damaged in stage tests with different intensities, so that the first spontaneous damage (local discoloration, sinter transfer) occurs. In the second step, an endurance test is carried out with the pre-damaged clutch packs and a non-pre-damaged reference clutch. The friction behavior of the clutches during the endurance test is compared and evaluated. It shows that local discoloration and sinter transfer are no longer visible after the endurance tests. At the beginning of the endurance test, the values of coefficient of friction are higher over the entire speed range of the heavily pre-damaged clutches than with the slightly pre-damaged clutch and the non-pre-damaged reference clutch. At the end of the endurance test, it can be observed that the greater the pre-damage to the clutches is, the greater the coefficient of friction increases with decreasing sliding speed. [ABSTRACT FROM AUTHOR]

Friction behavior in a sliding contact is strongly influenced by the surface topography of the bodies in contact. This also applies to friction clutches. Even small differences in surface topography may cause significant differences in friction behavior. Thus, it is important to be able to characterize the micro-contact of the rough sliding surfaces, which are, in the case of a clutch, steel plate and friction material. One important measure for the characterization of the micro-contact is the real area of contact. Another important aspect is the contact pattern. The article introduces a method to implement a FEM (Finite Element Method) model from real surface measurements. Real surface topography of the friction pairing is considered. The simulation method is applied to different friction pairings and operating conditions. Computational results with rough and smooth steel plates, new and run-in friction linings, and different nominal surface pressure verify the model. In addition, the results on real area of contact between a steel and a friction plate are compared with published values. [ABSTRACT FROM AUTHOR]