Research On Vehicle Economic Cruise Control Method Based On Transient Polynomial Fuel Consumption Model And Model Predictive Control

With the rapid development of automobile industry,the petroleum energy consumption in China increases dramatically.Thus,reducing the energy consumption of vehicles has become a hot topic in automobile industry in recent years.According to the existed research,there are four types of technologies to improve the fuel economy and reduce the fuel consumption in driving: engine and vehicle design optimization,economical driving technology,intelligent traffic management technology and new energy vehicle technology.According to the existed studies,economic driving strategy can help saving about 15% of fuel by improving driver's decision-making,and control of throttle,gear and brake.It has become an important development direction in automotive energy saving field.Because of its intelligent hardware system,automobile cruise system has become an ideal carrier of economical driving strategy,which can replace the driver to complete the driving task automatically.Economic cruise system can control vehicles to adopt fuel-saving driving strategy,thus maximizing the advantages of fuel-saving driving strategy.In summary,researches on vehicle economy cruise technology can help maximizing fuel economy in driving.Based on the working mode of the adaptive cruise system,this paper divides the automobile economical cruise system into two control modes according to whether there are front cars.Cruise control system will perform economic speed control if there is no front car.When there are vehicles in front,the cruise system will adopt multi-objective control to improve the fuel economy under the promise of safety following drive.According to the above two modes of economic cruise system research,the main research contents of this paper include the following four aspects:(1)Design of economical cruise control structure and system dynamics model establishmentThe economic cruise control algorithm in free-running mode and car-following mode is designed respectively according to the different control mechanism.The key technology of economical cruise control system is discussed in this report.The safety distance model of the workshop is established based on considering the movement trend of the front car.The longitudinal dynamic model between car-car is established.Among which,the front and back car distance error,relative speed and the acceleration of the vehicle are taken as state variables,the expected acceleration of the vehicle is taken as input,and the front car acceleration is taken as disturbance.In this part,the structure design of economical cruise system is the main stream of the paper,and the system dynamics model is the foundation of the economical cruise control algorithm.(2)Transient fuel consumption model and economic vehicle speed planning algorithmCombining with the economic speed optimization system requirements on fuel consumption model,this paper proposes a transient fuel consumption model based on analysis of the advantages and disadvantages of the existing fuel consumption models.Transient Polynomial Fuel consumption model(TPFM)is established based on the measured on bench fuel consumption data.The model is divided into two parts: steady-state fuel consumption model module and transient correction module.The steady-state module is based on the polynomial fuel consumption model,and it can be evaluated by Bayesian Information Criterion(BIC).The transient correction part uses the engine torque rate to modify the model,and the model accuracy can be evaluated based on the different real working situation statistics.Taking the lowest fuel consumption as the control objective,an economic speed optimization algorithm is designed based on the discrete dynamic programming algorithm under TPFM model.(3)Economic cruise control algorithm study under car-following modeThe control objectives of cruise system in car-following mode are analyzed.The economical cruise control system of automobile is designed based on the model predictive control(MPC)algorithm and the longitudinal dynamic model of car-car.Systematic cost function and constraint conditions is set in the foundation of safety car following.It also takes fuel economy,comfortability into consideration.In order to further improve fuel economy,a fuzzy logic algorithm is used to adjust the weight coefficient of the cost function and an adjustment strategy based on the movement state between the car-car is proposed.On the basis of modeling the control object and designing the performance index of the single-time cruise system in discrete state,the predictive model of each part of the model is deduced.The system optimization problem based on the predictive control quantity in time domain is established,and the algorithm design of the economical cruise controller for automobiles is completed.The application of model predictive control in application is analyzed for actual problems.The robustness of the model is improved by feedback correction method.The problem of infeasible solution is solved by relaxation factor based on constraint management method.(4)Experimental research on economical cruise control algorithmIn order to verify the effectiveness of the economic cruise control algorithm under the two modes proposed in this paper,experiments are designed to verify them.In order to test the fuel-saving effect of the economic speed control algorithm under the free-running mode,the ramp experiment and the actual road experiment are designed.In order to verify the validity of MPC control system based on variable weight in car-following mode,experiments are designed to simulate the actual scene of vehicle cruising process,and the control effects of variable weight model predictive controller and conventional model predictive controller are compared.The experimental results show that the economic cruise control algorithm in the two modes can provide the fuel economy of the cruise system.