| Summary: | A new permanent magnet retarder (PMR), which based on the principle of eddy-current braking, is proposed as an auxiliary braking apparatus for heavy vehicles. Its braking torque can be stepless adjusted by the adjustment mechanism. A multi-physics field coupling model of the retarder was established, which includes electromagnetic field, thermal field, and fluid field. The distributions of the three fields were calculated using the finite-element method. To predict the demagnetization of the permanent magnet, a new analysis method of the permanent magnet irreversible demagnetization is proposed, which uses the dynamic air-gap flux density simulated under various temperature B-H curves and the relationship between the braking torque, as well as the square of air-gap flux density. The braking torque and temperature rise of the PMR were tested on the bench. The bench test results show that the braking torque calculated by the multi-physics coupling method agrees better with the experimental data, and the high-temperature irreversible demagnetizations of the permanent magnet occurred by the enormous heat generated during continuous braking. The vehicle test results show that the braking distance can be shortened by 34% after using the PMR, and the braking deceleration is increased by 1.05 m/s<sup>2</sup>. The proposed PMR can meet the requirements of auxiliary braking for heavy vehicles.
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