Clutch systems with advanced ceramics under high load operating conditions
Prof. Dr.-Ing. Albert Albers
Institut für Produktentwicklung
Karlsruher Institut für Technologie
Goal of the TP A2 is the research of development methods and tools for suitable ceramic design as well as the integration and validation of friction materials in unlubricated, dry running friction systems using the example of a complex vehicle clutch. Specific characteristics of this friction system like variable sliding speed, average contact stress, variable specific energy input and specific frictional power lead to particular challenges in designing the demonstration system and in the interaction of the system development process and the material development process. Certain functionally relevant frictional pairs (ceramic/metal) and their realization in a complete system – in this case the demonstrator “dry running clutch” – will be researched, considering the specific requirements for dry running, highly stressed frictional contacts in view of the achievement potential (e.g. friction coefficient level and consistency, torque capacity), the wear potential (e.g. wear of functions, durability), and the comfort behavior (e.g. gradient of the friction coefficient, NVH-behavior).
A new design solution for the clutch disk (carrier of the ceramic friction materials) as well as the complete clutch system has been developed and successfully tested in the current funding phase. The complete simulation approach “CoupAction” has been realized according to the planned assignments. The thermo-mechanical stress of the clutch discs bearing the ceramic friction materials has been determined and linked sequentially to the calculations using the simulation tool STAU (TP C4). New testing concepts and modules for examining the friction system under contact stress on both sides have been developed in experimental work. They were used to perform basic analyses on the demonstration systems. Methodical research on the transferability between the testing levels has been pursued further. Results show that a qualitative transferability among the testing categories IV, V and VI exists, which is necessary for a methodical selection of suitable frictional pairs in the early phase of the development process. Based on the existing results, a procedure model for the friction system development of ceramic friction materials is to be developed in the upcoming development process phase. The model will combine testing methods from the categories I to VI and the hence determinable factors.
The experimental results regarding the dry clutch demonstration system show an increase of the power density by 49%. The desired level of the frictional factor was achieved by the newly developed frictional pair Ekasic-F/C45E. Experimental analysis showed that the clutch system’s wear reserve is insufficient under real boundary conditions and that the frictional factor gradient’s behavior (judder excitation) has yet to be improved. In the proposed funding phase the friction and wear potential of the clutch system is supposed to be increased to the target system’s necessary level of durability, with the help of constructive concepts and the material development of TB B2. The comfort behavior is to be improved with help of a hybrid approach (combination of ceramic and organic friction materials) in a system and a mechatronic clutch control meant to actively reduce judder vibrations. The procedure of developing the constructive hybrid approach as well as the active control will be generalized into methods at the same time and will then be implemented, together with TP A8, in the ceramic specific development process, containing the aspects of handling engineering ceramics. This way the hybrid approach for friction systems with ceramic materials can be used for future development tasks. Another important aspect supposed to be researched in the proposed funding phase is the permanent slip operation in a slipping range between 0.1 and 1 m/s. Those operation parameters are important for the active vibration damping in modern double clutch system solutions and can thus tap into further high potential of clutch systems with ceramic friction materials. These investigations will methodically expand the characterization of the friction system ceramic/steel by implementing the aspects of permanent slip. The mode of action in the frictional contact and the transferability among the individual testing categories will be researched as well. Thus an almost completed investigation method for dry running frictional contacts in complex technical systems will exist as part of the development process at the end of the funding phase and the investigated friction pairings will be characterized for the operating conditions “permanent slip” and “synchronization of drive trains”.