High frequency shifting clutch to reduce the friction losses during the synchronization process
Mechanics
Final Report Abstract
In this research project, analogies between electrical engineering and mechanics are used to develop a mechanical step-down converter. A corresponding prototype is built, tested on a highly dynamic powertrain test bench and successively developed further within the framework of the research project described here. The novel topology is to be used to reduce the high friction losses that occur in the slip-state of a frictionlocked single-disc dry clutch during a rotational speed synchronization process. To implement the "converting by periodic switching" approach from power electronics, a fast-shifting clutch and a mechanical energy storage system, consisting of torsional springs (in the form of spiral band springs) and flywheel masses, form the main elements of the mechanical step-down converter. Two objectives are pursued in order to optimize the system within the scope of the research project documented here: On the one hand, the clutch efficiency is to be increased. On the other hand, the rotational speed and torque oscillations on the output side, caused by high-frequency shifting, are to be minimized. To achieve these goals, in this project the hydraulic clutch actuation system in terms of both hardware and software is optimized in order to realize higher shifting frequencies. In addition, the energy storage element is expanded to a rotational dual-mass oscillator in the context of the reduction of its overall torsional spring stiffness. Up to a switching frequency of approx. 30 Hz, the highly dynamically actuated clutch can realize rectangular hydraulic pressure or rather contact force curves and thus achieve "clean" opening and closing processes without distinctive slippage. As a result, the rotational speed synchronization processes carried out at a switching frequency of 20 Hz have a significantly higher clutch efficiency of up to 85% compared to slipping clutch operation. In addition, the optimization measures implemented result in a significant reduction of oscillation effects at the output.
