Automatic Two-Speed Transmission Based on a Combined MRF Coupling Element

This article deals with the design and experimental investigation of an automatic two-speed transmission with a combined coupling element based on magnetorheological fluids (MRF). The gearbox consists of two planetary gears offering a mechanical power split to reduce the torque load on the coupling elements. For the control of the two-speeds, a combined coupling element is applied consisting of an MRF-clutch and an MRF-brake. The complete gearbox design, the numerical design of the combined MRF coupling element as well as the developed gear control based on a state machine are discussed in detail. The experimental investigation includes stationary and dynamic scenarios. The stationary analysis focuses on the torque transmission and drag torque, while the investigation of the dynamics deals with certain speed-changes to demonstrate the smooth and dynamic torque control without interruption of traction.