Research On Torque Distribution Control Strategy For Singleshaft ISG Hybrid Electric Vehicles

The design of control strategy for singleshaft ISG Hybrid Electric Vehicles is an importantpart in vehicle and subsystems controller development, and the foundation of achieving energysaving and emission reduction. This paper is supported by the energy saving and new energyvehicles major projects of National “The Eleventh Five-year Planning”, and torque distributioncontrol strategy for driving conditions, dynamic braking torque distribution control strategy,dynamical coordinated control strategy for regenerative braking with ABS system, and controlstrategy for enhancing the braking stability of Hybrid Electric Vehicle were researched, and rapidcontrol prototype simulation test of the proposed control strategy were implemented based ondSPACE real-time system. The main research work and conclusions were summarized asfollowing:In order to provide the simulation and verification foundation of the torque distributioncontrol strategy, Engine model, ISG model, batteries model and all condition tire model usingmagic formula were built based on experimental data, and power train model, hydraulic brakingsystem model, seven-DOF vehicle dynamics model and driver model were developed based onphysical logic of parameters.The fuel economy and emission performance function of the ISG Hybrid power system wasestablished based on the test data of internal combustion engine and ISG motor, and the data ofoptimal operating points for training ANFIS system was got by the method of searching globalminimum point of multivariable function. A torque distribution system for reasonably distributingthe vehicle’s demand torque of driving to the internal combustion engine and ISG motor based onthe trained ANFIS system was built for decreasing the fuel consumption and emissions. Theresults of simulation show that much better fuel economy and emission performance are achievedunder the ANFIS torque distribution control strategy than electrical assistance control strategy.A real-time computation method of optimal slip ratio acquisition for braking road conditionwas proposed. The braking road was confirmed by comparing the wheels achieved adhesioncoefficient with peak adhesion coefficient of typical roads, and optimal slip ratio of braking roadwas real-time searched by golden section method according to the function between adhesioncoefficient and slip ratio. A coordinated control strategy based on slip ratio control was designedfor dynamical distribution between regenerative braking torque and hydraulic braking torque. Thesimulation results show that braking energy can be high ratio recycled in mild-moderate brake,braking efficiency and braking safety were assured by avoiding wheel lock under emergencybraking condition. As the road condition is uncertain, the problem of optimal slip ratio estimation duringbraking was considered as a real-time self-optimizing problem of extremum drift, and a dynamicalcoordinated control method for regenerative braking with ABS system was proposed based on slipratio self-optimization. A fuzzy self-optimizing controller for optimal slip ratio control wasdesigned, and the fuzzy control rules were on-line optimized by a genetic algorithm. Regenerativebraking torque is preferentially adjusted to meet the adjustment demand of total braking torqueunder the state of emergency braking. The braking processes on high, low, mutative and splitadhesion coefficient road were simulated respectively, and results show that the proposed controlalgorithm not only can achieve optimal slip ratio automatically and rapidly, and regenerativebraking system is dynamically coordinated with Anti-lock braking system to ensure the brakingefficiency and braking stability, but also considerable braking energy can be regenerated under thestate of emergency braking.A hierarchical coordinated control strategy for enhancing the braking stability of hybridelectric vehicle equipped with a regenerative braking system and a hydraulic braking system wasproposed. The desired yaw moment compensation was formulated with a preference toregenerative braking torque and wheels slip ratio control during braking process. The upper-levelyaw moment control was coordinated with lower-level wheels slip ratio and regenerative brakingtorque control by the nominated target slip ratio. Simulation was performed under low and highadhesion coefficience road with cornering, and the results show that the hybrid electric vehiclewith the hierarchical coordinated control strategy not only can keep good Braking efficiency, butalso achieves better performances of dynamic braking stability than the vehicle only with slip ratiocontrol.Finally, the proposed torque distribution control strategy was further verified and perfectedby Rapid control prototype test.