Wear compensation systems for dry clutches How clutch actuation is affected by wear and how a wear compensation system can be implemented to make clutch operation more consistent

Examensarbete för masterexamen
Automotive engineering (MPAUT), MSc
Bergqvist, Sven
Abrahamsson, Patrik
With the environmental pollution becoming a greater concern one way to reduce emissions is to switch from vehicles with fossil fuel driven internal combustion to battery electric vehicles. This type of vehicle become increasingly popular and the demand for higher total energy efficiency and performance of the vehicle is es sential for the customers. One way to do this is to implement a two-speed gearbox with a dry normally open friction clutch controlled by an electrical actuator. During the lifetime of the vehicle an axial wear of the clutch will occur and result in a need for different displacement and/or forces to operate consistently. To lower or eliminate this problem a wear compensation system is implemented. To understand the type and amount of wear, the theories behind this was investigated. Using existing data from several sources the total axial wear of the dry friction clutch was calculated to be 2.15 mm over the complete life cycle. The next step was to find existing wear compensation solutions. This was done searching through patent databases and through information from the company AVL MTC which are the stakeholder in this thesis. The evaluation of these solutions resulted in a few concepts that was categorised and selected for further analysis. This investigation resulted in schematics and evaluation of their respective functions. When the design of the complete clutch system based on the requirements and specifications was done, only a few of these concepts was determined to work properly without major redesign. Due to the time limitation one of these concepts was chosen to investigate further. This concept is called the Rod and Nut concept which rotates a nut when wear is present. This motion will increase the length of the rod because of the threads on the rod and nut therefore compensating for the change of displacement needed when the clutch is worn. This compensation procedure will happen when the actuator goes further compared to the normal operation, called the wear check cycle. The actuator will overload the system compared to the normal actuation using a predetermined force. Due to the design of the mechanism it will only compensate if the axial wear is large enough, that is due to the extended travel to reach that predetermined force when the clutch discs are worn. This is something necessary for this design and this procedure is preferably done when parking the vehicle and turning it off after everything is up to temperature from driving. The potential benefits of a compensation system like this, proved to be promising both regarding actuator requirements and actuation consistency. It also become clear that the actuation time performance could be improved significantly throughout the life cycle, using the same actuator power.
wear compensation systems, dry clutches
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