In order to improve the torque to volume ratio of magnetorheological （MR） brakes, a MR brake with internal and external fluid flow channels was developed.

Firstly, the structure and working principle of the MR brake with internal and external fluid flow channels were introduced, and the mathematical model of the braking torque was established based on Bingham constitutive model. Secondly, in order to obtain the optimal structure size of the MR brake, structural optimization design was carried out based on the non-dominated sorting genetic algorithm (NSGA-Ⅱ). Finally, the prototype of MR brake was fabricated, the torque performance test system was built, and the braking performance test was conducted for the MR brake.

There are both internal and external fluid flow channels in the MR brake. Six effective damping gaps are obtained by reasonable setting of magnetic conductive and magnetic isolating materials in the MR brake, so that it can produce excellent torque performance under the premise of the same size. The theoretical calculation results show that the braking torque and the adjustable range after optimization are increased by 30.23% and 16.58% respectively compared with those before optimization. Test results show that at the applied current of 2.0 A, the maximum braking torque is 44.28 N·m, and the dynamic adjustable range is 17.8. The relative errors of the braking torque and the dynamic adjustable range between the test values and the theoretical calculation values are 6.5% and 16.1% respectively, which verifies the rationality of the design.