Research on Thermal Management of Magnetorheological Fluid Retarder Based on Phase Change Principle 2020-01-0948

In order to avoid the braking recession on heavy commercial vehicles caused by the long-distance continuous braking of the main brake, the hydraulic retarder is widely used as an important brake auxiliary device in various heavy commercial vehicles to improve the vehicle safety. However, the hydraulic retarder not only has the advantages of large braking torque and good stability, but also has the disadvantages of poor retarding ability at low rotating speed, braking lag and difficulty in accurately controlling the braking torque. This paper introduces a new type of hydraulic retarder. The new retarder replaces the oil in the retarder with magnetorheological fluid and applies a magnetic field in the retarder arrangement space, so that slows down the vehicle by using the rheological properties of the magnetorheological fluid under the magnetic field. The magnetorheological fluid hydraulic retarder (MRFHR) generates a large amount of heat during working which not only decreases the braking performance, but also causes the structure to be damaged, and even risks the safety of the driver and the vehicle. This paper studies on the thermal characteristics of the magnetorheological fluid hydraulic retarder. Base on the thermal characteristics, a heat dissipation system is designed by the phase change principle to improves the working stability of MRFHR and the uniform of temperature distribution. By the one-dimensional beam theory of hydraulic retarder and the working mode of magnetorheological fluid, the thermal model of magnetorheological fluid retarder is established under different the magnetic field. The shear force model under axial and circumferential magnetic fields is established when the retarder works. The heat generation power of the magnetorheological fluid retarder is simulated for axial and circumferential magnetic fields. The result shows that the heat generations power of the retarder increases with the increase of the axial magnetic field, decreases when the circumferential magnetic field rises. An experimental study on the temperature distribution characteristics of the outer wall surface of the retarder shows that the wall temperature distribution is affected by the radius and gravity, and the temperature difference also increases with the increase of rotational speed. Combined with the thermal characteristics of MRFHR, a cooling system based on phase change principle was designed and the thermal management system was verified. The results show that the cooling system reduces the working temperature of the retarder wall and improves the uniform of temperature distribution.