Strategy Identification And Operation Rules Of Vehicular Economical Driving

Energy security and environmental protection continuously push the automotive industry to reduceenergy consumption and emission.The fuel-minimized economical driving technique isbecoming a promising approach to solve the problem.Arising from the strong nonlinearity,discrete control inputs,and mode switching of the engine and powertrain,the vehicle dynamic is actually a nonlinear mixed integer system,which makes the eco-driving strategies difficult to be solved and thus leads to the lack of effective fuel-saving rules.To conquer the problem,this paper(1)establishes a universal methodology in the dimensions of “framework,algorithm,and numerical solver” to quantitatively obtain eco-driving strategies;(2)studies the fuel-saving strategies,underlying mechanisms,and control laws under threetypical scenarios,i.e.,accelerating,cruising,and running on varying slope.To efficiently obtain eco-driving strategies for different types of vehicles and scenarios,this paper proposes an idea that converts “identification of eco-driving strategies” into “optimal control problem”,and then constructs an optimal control based framework.To solve the thorny problem with strong nonlinearity,discrete control inputs,and mode switching,the Legendre pseudospectral method combining with the multi-phase knotting strategy is employed and improved,and a universal numerical solver called POPS is developed,which realizes the solving of the mixed integer eco-driving problem with spectral accuracy.This paper studiesthe fuel-saving accelerating strategy for vehicles with discrete transmission speed ratio.We propose a new index called as equivalent fuel consumption to evaluate the fuel economy of different accelerating operations;numerically solve the mixed integer eco-accelerating problem by applying the pseudospectralknottingmethod andthe sequential shift rule.It is found that theoptimal accelerating operation is “stairway type” control,i.e.,the profile of acceleration versusvehicle speedappears as a stairway.The reason is that the eco-accelerating behavior is dominated bythe engine fuel efficiency;the stairway type acceleration could maximize the system efficiency.For free cruising scenario,the fuel-minimized operation laws and their mechanismof conventional vehicles with AMT and parallel hybrid electricalvehicles(HEVs)are studied.The studies find that the optimal cruising operation of the AMT vehicle is periodic accelerating and coasting(PnG),essentiallyarising from the engine's discontinuous S type fuel feature;for parallel HEVs,the eco-operation has two modes: speed fluctuating mode and SOC fluctuating mode.Their fuel-saving capacities arise from that both the battery and the vehicle body can act as energy buffer,whose periodic charge and discharge could make the engine run in high-efficiency areaintermittently,thus improvedthe system average efficiency.To economically driving on varying slope,this paper develops two real-timefuel-prioritized controllers,i.e.,steady-state relied controller(SRC)and kinetic energy conversion controller(KEC).The former is derived from theminimum principle with an estimatedHamiltonian,and the latteris designed based on equivalent conversion between the kinetic-energy change of vehicle body and the fuel consumption of engine.Both of them have nonlinear analyticalcontrol laws and could highly impove the computational efficiency,and achieve a good performance with computing time under onemillisecond in each step while without deteriorating fuel economy.