Study On Energy Saving Mechanism And Control Strategy Of Hybrid Electric Bulldozer

Bulldozer,having characteristics of low energy efficiency,high fuel consumption and severe emissions,is an important technical equipment in the national infrastructure construction.As energy shortage and environmental pollution problems becoming more seriously,energy conservation and emission reduction of bulldozers have been concerned widely.Because hybrid technology has been recognized as one of the best solutions for energy conservation and pollution reduction,therefore,it is of great practical significance to carry out the research on hybrid technology of bulldozer.This dissertation took hybrid electric bulldozer as the research object and emphatically foucesd on four aspects including the operating cycle,whole simulation model,energy saving mechanism and control strategy.The research on the development of hybrid electric bulldozer operating cycle was carried out,and a method to develop representative operating cycle for hybrid electric bulldozer based on-board data was proposed in this dissertation.The data collection experiment of operating cycle for hybrid electric bulldozer was conducted;the parameters to characterize operating cycle were selected;the parameters of track type bulldozer dynamics model were identified by adopting the least square method;the operating cycle overall data set were obtained through using dynamics and kinematics models to caculdate CAN(Controller Area Network)bus data;the characteristic parameters set of operating segment were put forward;the smallest Mahalanobis distance as a criterion was proposed to select representative operating segments,a representative operating cycle of hybrid electric bulldozer was developed finally.The validation showed that the developed representative operating cycle was consistent with the overall condition data set on the joint probability distribution,and the error was about 2.1%in terms of fuel consumption,indicating that the developed cycles was significant representative and effective.A hybrid electric bulldozer model,including the drivetrain components’ models,tracked bulldozer dynamics models,driver model and bulldozer controller unit model,was established based on Matlab/Simulink.A modified engine fuel consumption model was proposed and developed based on BP neural network,and a hydraulic pump model was established.The simulation effect and performance of the developed model was validated and tested by using field experiments of a hybrid electric bulldozer.The results showed that the developed model could accurately simulate the hybrid electric bulldozer performance in straight and steering conditions,and could also simulate engine transient fuel consumption and the influence of the working device hydraulic system on the working process and control effect of power system.The energy saving mechanism problem of hybrid electric bulldozer was studied,and a new energy saving mechanism analysis method based on analytic method was proposed in this dissertation.The analytical expression of the equivalent fuel saving ratio of hybrid electric bulldozer,which expressed the functional relation between the equivalent fuel saving ratio and its influence factors,was built in this method.Through performing energy consumption simulation and calculation by using hybrid electric bulldozer and traditional bulldozer model,combined with the energy consumption simulation data and the analytical formula,the energy saving mechanism of hybrid bulldozer can be revealed.By using this method,the energy saving effects of hybrid bulldozer were analyzed,and the key influence factors and approaches of energy saving were revealed,the contribution rate and potential of energy saving were obtained.Frequent fluctuation of the engine working points could lead to higher transient fuel consumption when the genset follows the fluctuant demad power.Genset working points would deviate the target working trajectory due to sluggish transient response when the change rate of genset output power is large.Also,genset working points would deviate target working trajectory due to the engine torque consumed by the hydraulic pump.To solve these three problems,the control strategy of the hybrid bulldozer was researched.Coupling the power following control strategy with fuzzy adaptive filtering algorithm and optimal efficiency Map of genset,the adaptive smoothing power following control strategy based on optimal efficiency Map was proposed in this dissertation.By applying the dSPACE real-time simulation system,a hybrid electric bulldozer controller unit hardware in the loop test platform was established.Through the hardware in the loop test,the control performance and energy saving effect of the adaptive smoothing power following control strategy based on optimal efficiency Map were verified.The analysis of test results showed that the control strategy proposed can achieve the desired function of real-time control of hybrid electric bulldozer;compared with the traditional bulldozer,the hybrid electric bulldozer could obtain the equivalent fuel saving ratio of about 23.2%by adopting the control strategy proposed;compared with the original control strategy used in the experimental hybrid electric bulldozer and power following control strategy based on the lowest fuel consumption rate curve,the proposed control strategy reduced the transient fuel consumption,and improved the switching process and distribution of genset working points,and the equivalent fuel saving ratio was increased by about 7.8%and 3.4%respectively.