Abstract
Drag losses in the powertrain of hybrid electrical vehicles are a serious deficiency for an energy-efficient application. A promising approach for fulfilling requirements like efficiency, wear, safety and dynamics is the use of an innovative clutch design for the transmission of power is based on magnetorheological fluids (MRF). MRF are smart fluids that exhibit the unique property of significant changes to apparent viscosity in the presence of an externally applied magnetic field. This property permits the design of novel mechanical devices for torque transmission such as brakes and clutches that offer continuously adjustable and smooth torque generation. In this paper, a novel clutch concept is presented that facilitates the controlled movement of the MRF from an active, torque-transmitting region into an inactive region of the shear gap. This concept enables complete decoupling of the fluid engaging surfaces such that viscous drag torque can be eliminated. Therefore, a methodology for designing such MRF-clutches is presented, which considers in detail the required magnetic excitation systems for enabling a well-defined safety behavior by the MR-fluid control. In particular, novel approaches for a shear gap design will be introduced that increase the torque capacity of the clutch. By the use of a micro-grooved structure, which is part of the magnetic excitation system, a much higher torque-to-volume ratio can be achieved, which is in the order of typical MRF-based actuators for torque-transmission with completely filled shear gaps. Newly developed approaches investigated by use of valid simulations underline the aimed improvements of the torque capacity by the novel micro-grooved structure for MRF-clutches. These actuator approaches are enabling the design of innovative coupling devices with sophisticated functionalities like a well-defined safety behavior for the use in the powertrain of hybrid electrical vehicles.
KEYWORDS – magnetorheological clutch, drag losses, torque control, high rotational speed, hybrid electrical vehicles