Research On Eddy Current-Hydrodynamic Hybrid Retarders For High Speed Tracked Vehicle

The heavy-duty tracked vehicle,which is developing towards high speed and maneuverability,has greatly reduced the service life of friction brake systems due to the huge brake energy.It is urgently needed to match them with a high-efficiency and fast-response non-contact auxiliary braking system to share the braking load of the main brake.At present,the braking power density of the eddy current braking and hydraulic braking is low,which is difficult to meet the braking demand,and the military highperformance hydraulic braking has high requirements for additional auxiliary systems,such as large-flow oil circuits and the energy storage,which make the system more complex and less reliable.Theoretically the characteristics of the eddy current braking and hydraulic braking are complementary.If they are designed as a whole,a hybrid retarder with large torque at full speed and rapid response will be obtained.Because of its fast response,the hybrid retarder can consume part of the braking load when the vehicle is braking urgently;when the vehicle is downhill for a long time,the hybrid retarder works alone and continuously consumes the mechanical energy of the vehicle.In this paper,the technical route combining theoretical analysis,finite element calculation and experimental verification is used to deeply study the working principle,design method,external braking characteristics,thermal analysis and vehicle braking dynamics of the hybrid retarder.The specific research content is as follows:Firstly this paper summarizes the basic theories of electromagnetic field,fluid dynamics,and heat transfer involved in the hybrid retarder,which lays the foundation for the establishment of the finite element model.At the same time,the equivalent magnetic circuit method,Maxwell's equation and one-dimensional beam theory are used to establish a semi-analytical model in order to deeply analyze the principles of eddy current braking and hydraulic braking.In structure,three hybrid retarders are designed,which are the radial structure hydraulic-eddy current hybrid retarder with hydraulic braking as the mainstay,the embedded structure eddy current-hydraulic hybrid retarder with eddy current braking as the mainstay and the highly fused eddy current-hydraulic hybrid retarder.In addition,an internal cooled eddy current braking is designed to study the continuous braking characteristics.The finite element calculation model are established to calculate the braking performance of the eddy current braking portion and the hydraulic braking portion.Comparing with the test results,the calculation error of the eddy current braking electromagnetic field finite element model considering the number of grids,calculation time steps and temperature factors is reduced to 5.3%-6.6%.The thermal derating of the eddy current braking torque is analyzed emphatically.Based on the finite element analysis,the reason of the above phenomenon is the decrease of the electrical conductivity and magnetic permeability of the stator material and the current of the excitation coil.The steady-state and transient-state magnetothermal coupling model of bidirectional data transmission is established to numerically simulate the continuous braking characteristics of the eddy current braking torque;the thermal-structural coupling model is established to optimize the size of the eddy current braking air gap;three sets of magneto-thermal coupling model comparison cases are established,and the calculation accuracy of transmitting heat generation rate,temperature,and convection heat dissipation coefficient by using the lumped parameter mapping method is analyzed.In addition,it is proved that the heat dissipation effect of the internal cooling is better than that of the water jacket using the established steadystate magneto-thermal coupling model.The vehicle dynamics model is established to simulate the braking process using the hybrid retarder,pure eddy current braking and pure hydraulic braking in three environments of benches,tracked vehicles and wheeled vehicles.On downhill roads,the hybrid retarder enables larger vehicles to cruise at lower speeds.When a vehicle is driving down a 7% slope and its speed drops from 80 km/h to below 35 km/h,the braking time of the hybrid retarder is the shortest.Finally,the braking bench test has been carried out on two hybrid retarders and two eddy current braking.The test data shows that the braking torque of the radial structure hydraulic-eddy current hybrid retarder is only slightly smaller than that of the pure hydraulic retarder at high speed;and the embedded structure eddy currenthydraulic hybrid retarder exhibits braking advantages at full speed.In addition,by increasing the excitation voltage to 48 V,the response time for the eddy current braking to reach 80% of the rated braking torque is 0.28 seconds,which is shorter than that of the friction brake.