Study On Key Technologies Of Self-excited Retarder

The self-excited retarder is a kind of energy-saving retarder which integrates modern generation technology and eddy current braking technology. In the braking process, it could transform automotive inertial energy into electric energy and provide excitation current for the retarder unit by itself. So the self-excited retarder is free from additional energy consumption. As a new type retarder, however, some key technologies, such as generation performance, braking torque caculation and control, rotor temperature field distribution with time etc. are relatively backward.Generation performance of a self-excited retarder determines whether the design goal of braking torque could be achieved. Transient electromagnetic field equation, field-circuit coupled equation and its discrete model about space and time were established and derived. On this basic, transient electromagnetic field of generation unit was caculated with Finite Element Method and the generation performance of a self-excited retarder was analyzed.Braking torque as one of the most important design goals, the calculation formulae for braking power and braking torque are detailedly derived based on the Electromagnetic Induction Law and the Maxwell’s Law. When automotive inertial energy was transformed into electric energy by generation unit, tangential electricomagnetic force (EMF) acting on the rotor would produce certain braking torque that is so-called electromagnetic torque. Flux method and Maxwell tention which are two common methods for caculating electricomagnetic torque were presented detailedly in paper. All above caculation formulae described the relation between braking power or braking torque and structural parameters of a self-excited retarder. And this would lay a theoretical foundation for the design and performance analization of a self-excited retarder.Because the mechanical structure of a self-excited retareder is more complex than other eddy current retareder, thermal design is especially important. Study on rotor transient temperature field distribution and how it changes with time not only are the theoretical basis for thermal design but also provide reference for closed loop fuzzy control of the braking torque based on rotor temperature difference and temperature difference ratio. Rotor transient temperature field, as well as boundary condition, was modeled and the caculation formula of inner heat source intensity was derived from braking power. Based on these models and caculation formulae, rotor transient temperature field distribution and how it changes with time were obtained with Finite Element Method and the error causes between theoretical and experimental results were analyzed.Control methods of a self-excited retarder braking torque were studied too. When rotor temperature is low, the main brake pedal pressure was taken as input variable and SCR conduction angle taken as output variable, controler would run at open loop fuzzy control model so as to provide as possible as the expected braking torque. As far as rotor high temperature is concerned, the usual processing method is to set up a threshold temperature. If rotor temperature is higher than the threshold, retarder would stop work so as to avoid possible scratch brought by high temperature expansion between rotor and stator. However, this would inevitablly lead to sudden acceleration and risk the road safty especially for a vehicle running on the long downhill mountain road. To this question, rotor temperature difference and temperature difference ratio were taken as input variables and SCR conduction angle variation was taken as output variable, closed loop fuzzy control would be selected if rotor temperature exceeds the threshold temperature. Fuzzy controllor would realtimely regulate SCR conduction angle variation and bifittingly reduce brake power, instead of simply stopping retarder work. So above sudden acceleration and risk would be avoided and road safty would be be greatly improved.Practices have proved that retarder has changed the vehicle’s existing braking force distribution. Impact on vehicle braking stability brought by retarder were analized from the braking force distribution, utilization adhesion coefficient and adhesion efficiency. Matching relation between the braking force distribution ratio and retarder braking force was studied based on the ECE_R13 Law and the optimal design of the braking force distribution ratio of a vehicle was put forward after installing retarder.