Magnetorheological Actuators with Currentless Bias Torque for Automotive Applications

The control of door motion in automotive applications often requires a bias torque to retain an actuator mechanism in a certain position without supplying power. Therefore, two magnetorheological actuators based on magnetorheological fluids with different kinds of magnetic excitation are developed. For the currentless bias torque generation, the first approach uses permanent magnets and offers an almost linear torque characteristic, while the second actuator design utilizes hysteresis properties of magnetizable materials resulting in an ambiguous control characteristic. The main advantage of the hysteresis-based magnetorheological actuator is an optimized design with respect to space and weight. But the hysteresis phenomenon has to be compensated by appropriate control algorithms, in order to obtain a linearized torque characteristic as investigated for actuated car doors with haptic capabilities (door assistant), such as for assisted egress or obstacle avoidance.