Research Of The Integrated Control Strategy For Fuel Consumption And Emission Of Full Hybrid Vehicle

The engine’s frequent start/stop of full hybrid vehicle dropped the temperature ofcatalytic converter and emission exhaust in urban driving cycle. As a result, thethree-way catalyst’s efficiency was lowered and the vehicle’s emission performance wasdecreased. Hybrid vehicle was equipped with two power sources, which were engineand electric motor. As an auxiliary power source, the motor can output or generatepower, which can optimize the engine’s operation under the premise of the powerrequirements. In this way, the increase of the three-way catalyst’s light-off was providedwith flexible measures in order to reduce the engine’s emission during cold start stage.The high-capacity batteries and high voltage facilities in hybrid electric vehiclessupplied the catalyst with high-power external heat source which offered a new solutionto decrease the emission. Therefore, the research of the integrated control strategy forthe hybrid vehicle’s fuel consumption and emission have important practicalsignificance for decreasing fuel consumption and emission exhaust furtherly, especiallythe emission during catalytic converter’s cold start stage.The paper took the dual clutch full hybrid vehicle (DCFHV) as the object of study.In order to improve fuel economy and decrease emission during cold start, the energymanagement strategy had been designed and then optimized. The specific studies weresummarized as follows.(1) The full hybrid vehicle’s mathematical model had been established. Both theengine model which can calculate torque and fuel consumption as well as emission, andthe three-way catalyst reflecting the catalytic efficiency had been established based onthe engine mean value theory and the thermodynamics law. Based on classic vehicle’slongitudinal driving dynamics, the model of vehicle’s cold start emission in NEDCdriving cycle had been established, which includes a mechanical automatic transmissionshifted by economy schedule.(2) The multi-objective global optimization of the fuel consumption and emissionof hybrid vehicle had been proposed by means of dynamic programming algorithm. Themathematical model of optimal controller for full hybrid vehicle had been established.Focusing on the characteristic of the engine’s frequent start/stop when the DCFHEV’soperation modes changed, the additional fuel consumption caused by engine’s star/stopwas considered in the model. After that, the optimal control problem of the hybrid vehicle in the specific driving cycle was converted to a single-step, multi-stage decisionproblem. According to the Bellman principle, a recursive equation was created and thencalculated using the dynamic programming algorithm to obtain the optimum controller.Finally, the optimal control variables were transferred into the vehicle dynamic modelforwardly to obtain the optimal state variables and the optimal value of objectivefunction.(3) The real-time control strategy for multi-objective optimization of hybridvehicle’s fuel consumption and emission had been established. In order to accelerate thecatalytic converter’s light-off, the fuzzy logic control strategy was presented. Controllercan reduce the cold start emission through improving the engine’s exhaust temperature.The electric heated control strategy which took advantage of the high power capacitybattery in hybrid vehicle to increase the catalytic converter’s light-off was proposed aswell. The equivalent fuel consumption of the battery in EHCS (electrically heatedcatalyst system) during cold-start was calculated. Some of the effects of EHCS’s heaterpower and location had been analyzed such as catalytic converter’s temperature andlight-off, HC/CO emission, equivalent fuel consumption and vehicle’s operating mode.In order to accelerate catalytic converter’s light-off and reduce fuel consumptionrespectively, the corresponding time shortest and fuel optimum control strategy wereapplied for different extrem objective function to obtain different optimum controlstrategy in according to the Pontryagin Minimum Principle.(4) The multi-objective stochastic linear optimal control strategy for fuelconsumption and emission of hybrid vehicle was established. On the basis of analyzingthe data collected along a fixed road, the actual driving cycle was equivalent to thesuperposition of a standard driving cycle with white noise interference. Thus control offuel consumption and emission for hybrid vehicle under actual road condition wastransformed to the optimal control in a standard driving cycle interfered with randomwhite noise. The quadratic state equation of full hybrid vehicle with three-way catalyticconverter’s temperature status was created. The multi-objective optimization functionwhich consists of engine’s fuel consumption and catalytic converter’s outlet emissionwas solved by stochastic linear quadratic optimal control method. The battery SOC(state of charge), speed, the actual state of the catalytic converter’s temperature andoutlet’s emission was estimated by Kalman filter so as to the optimal feedback of motoror engine power and other output variables can be realized. The optimal control strategyof the fuel consumption and emission of hybrid vehicle can be achieved therefore. (5) The tests of dual clutch full hybrid vehicle’s powertrain in test rig had beenaccomplished. The hardware-in-loop experiment test rig of the powertrain was set up.The test model based on the MATLAB/Simulink/dSPACE platform was founded andthe corresponding data acquisition and controller was developed. Some tests foroptimization of fuel consumption and emission in specific working mode such ascombined driving had been finished in the test rig. The accuracy and effectiveness of thesimulation and part of the control strategy of hybrid vehicle had been verified byexperiment results.