Power-split Hybrid Powertrain Research Articles

Optimization of intelligent charge compression ignition engine in hybrid electric powertrain by adaptive equivalent consumption management strategy

Dual fuel intelligent charge compression ignition (ICCI), taking advantage of two direct injection fuel supply systems, substituted low-carbon fuels for conventional fuels, improving fuel economy and emissions. This study focused on the application of the ICCI engine on the power-split hybrid powertrain and carried out the influence of the real-time energy management strategy on ICCI engine performance. Taking the ideal solution calculated by dynamic programming (DP) as the benchmark, equivalent fuel consumption minimum strategy (ECMS) and adaptive equivalent fuel consumption minimum strategy (AECMS) were compared in aspects of ICCI engine performance and state of charge (SOC) control robustness. The results showed that AECMS had better performance on SOC control, where the maximum deviation from the ideal control by DP was lower than 0.5 % during the charge sustaining stage, and the maximum deviation during the charging and discharging stages was no more than 1.5 %. In terms of engine performance control, the accumulative fuel consumption increased by no more than 20 %, and the average E85 (85 % ethanol in ethanol-gasoline blend) substitution ratio reduced by less than 8 %. Despite consuming a high proportion of E85, the accumulative fuel mass consumption of the hybrid powertrain was still 4 % lower than the conventional diesel vehicle.

Analysis and design of multi-mode power split hybrid transmission scheme considering mode connection

For heavy-duty truck, multi-mode power split hybrid transmission scheme (MPSHTS) has good adaptability. However, the moment of inertia at both ends of the clutch is large. If there is a large speed difference in the clutch engagement process, it will increase clutch wear, engine stall and other problems. This paper proposed a new design method of multi-mode power split hybrid powertrain, which was different from the proof by exhaustion aiming at mode switching without speed difference. It included: the conditions for achieving mode connection without speed difference was obtained based on the lever method for dynamic characteristic analysis. Evaluation index for power split mechanisms that comprehensively considered power source and transmission system was established. Combining the mode connection conditions and the optimized basic configuration, the characteristic of no speed difference could be ensured by adjusting the power coupling mechanism. A multi-mode scheme based on optimized configuration and work mode requirements could be obtained. Finally, parameter matching and simulation verification on the designed scheme was carried out. It suggested that the designed system improved fuel economy by 4.14% compared with the original scheme.

LSTM-based energy management algorithm for a vehicle power-split hybrid powertrain

Recurrent neural networks (RNNs) have been used for vehicle speed prediction, trajectory prediction and state diagnosis. As a variant of RNNs, long short-term memory (LSTM) has better state memory ability to deal with problems that have sequential characteristics. In this study, a neural network with two substructures was developed and LSTM was used as the core part for a power-split hybrid powertrain energy management problem, and the optimal control data obtained from the dynamic programming (DP) algorithm was used as the training set. Then on a vehicle model established on coasting-down test data, LSTM conducted real-time control. This paper analyzes the battery status, fuel consumption, carbon dioxide emissions and operating condition of the engine and motor. The results showed that LSTM has good generalization ability and real-time control capability. In the test driving cycles of CHTC-LT and C-WTVC, the theoretical optimal scheme given by the DP algorithm is only 12.15% and 17.96% lower than the LSTM scheme in terms of fuel consumption. In addition, the influence of network size, training epochs and training set on energy-saving effect is compared in detail, it was found that the relatively optimal model required 128 LSTM layer units and 500 training epochs.

MPC-Based Coordinated Control of Gear Shifting Process for a Power-split Hybrid Electric Bus with a Clutchless AMT

Two-speed clutchless automated manual transmission (AMT) has been widely implemented in electric vehicles for its simple structure and low cost. In contrast, due to the complex response characteristics of powertrain, utilizing clutchless AMT in a hybrid power system comes with complex coordination control problems. In order to address these issues, a power-split hybrid electric bus with two-speed clutchless AMT is studied in this paper, and a coordinated control method based on model predictive control (MPC) is used in gear shifting control strategy (GSCS) to improve gear shifting quality and reduce system jerk. First, the dynamic model of power sources and other main powertrain components including a single planetary gear set and AMT are established on the basis of data-driven and mechanism modeling methods. Second, the GSCS is put forward using the segmented control idea, and the shifting process is divided into five phases, including (I) unloading of drive motor, (II) shifting to neutral gear, (III) active speed synchronization by drive motor, (IV) engaging to new gear, and (V) resuming the drive motor’s power, among which the phases I and V have evident impact on the system jerk. Then, the MPC-based control method is adopted for these phases, and the fast compensation of driving torque is realized by combining the prediction model and quadratic programming method. The simulation results show that the proposed GSCS can effectively reduce shift jerk and improve driving comfort. This research proposes a coordinated control strategy of two-speed clutchless AMT, which can effectively improve the smoothness of gear shifting and provides a reference for the application of two speed clutchless AMT in power-split hybrid powertrains.

Improved multi-dimensional dynamic programming energy management strategy for a vehicle power-split hybrid powertrain

Dynamic programming is a widely used algorithm to solve the optimal control problem for hybrid electric vehicle in the whole driving scenario, but the problems of interpolation error and dimensional disaster have not been completely solved. This study proposes an adaptive adjustment method to solve the interpolation error problem, in which the solution without theoretical error can be obtained at the cost of a tiny driving cycle accuracy. Furthermore, a dynamic equivalent consumption factor calculation method is proposed to analyze the change of energy storage quality in the battery pack and the instantaneous equivalent consumption of the motors. The effectiveness of the improved algorithm is verified on a passenger car with hybrid powertrain using planetary gear mechanism. The results show that the established multi-dimensional dynamic programming algorithm has a relatively stable energy-saving ability. The maximum gap of fuel consumption rate is 3.2% in the four test driving cycles. Besides, there is only a maximum difference of 0.29‱ between the original driving cycles and the new cycles generated by the adaptive adjustment method. And obvious dynamic equivalent consumption factor changes of 15.7% in WLTC-class3, 10.3% in CLTC-P, 11.8% in FTP75 and 11.0% in NEDC are observed through the proposed calculation method.

Multi-Objective Design Optimization of a Novel Dual-Mode Power-Split Hybrid Powertrain

This paper aims to explore the performance potential of a novel dual-mode power-split hybrid powertrain. First, the steady-state power split characteristics for the proposed hybrid powertrain in different modes are analyzed. The mode switching strategy is developed to maximize powertrain efficiency, which is verified by using dynamic programming based on direct transmit points (DTPs). Moreover, a novel multi-objective evolutionary algorithm based on the decomposition (MOEA/D) method used in a nested way with dynamic programming is proposed to solve the multi-objective optimization of the PS-HEVs for the first time, and the computational efficiency and superiority of the proposed algorithm is compared with the commonly used NSGA-II algorithm. The results show that the MOEA/D based multi-objective optimization framework has similar performance in the search for the Pareto frontier but significantly higher computational efficiency than that of the NSGA-II algorithm. The obtained Pareto frontier provides optimal design candidates for hybrid powertrain systems.

Review and Development of Electric Motor Systems and Electric Powertrains for New Energy Vehicles

This paper presents a review on the recent research and technical progress of electric motor systems and electric powertrains for new energy vehicles. Through the analysis and comparison of direct current motor, induction motor, and synchronous motor, it is found that permanent magnet synchronous motor has better overall performance; by comparison with converters with Si-based IGBTs, it is found converters with SiC MOSFETs show significantly higher efficiency and increase driving mileage per charge. In addition, the pros and cons of different control strategies and algorithms are demonstrated. Next, by comparing series, parallel, and power split hybrid powertrains, the series–parallel compound hybrid powertrains are found to provide better fuel economy. Different electric powertrains, hybrid powertrains, and range-extended electric systems are also detailed, and their advantages and disadvantages are described. Finally, the technology roadmap over the next 15 years is proposed regarding traction motor, power electronic converter and electric powertrain as well as the key materials and components at each time frame.

Estimation of Transmission Input&Output Shaft Torque and Drive Wheel Speed for Compound Power Split Powertrain Based on Unknown Input Observer

Precise estimation of transmission input&output shaft torque and wheel speed is significant to the development of torque distribution and coordinated control method for the power split hybrid powertrain system. This paper studies an estimation method of transmission input and output torque as well as drive wheel speed using an unknown input observer in different operating modes for a compound power split hybrid powertrain system. Firstly, the configuration and dynamic characteristic of power split transmission is analyzed. Then, state equations in different operating modes are established, and a Takagi-Sugeno (T-S) fuzzy model is utilized to deal with the nonlinearities of load resistance torque. Furthermore, an unknown input reduced-order observer is designed to estimate the transmission input&output shaft torque and wheel speed. The asymptotical stability of the developed observer is verified based on Lyapunov theory. Finally, the performance of the unknown input observer is assessed by comparing with the Luenberger observer based on Matlab/Simulink simulation platform and test bench. Simulation and experiment results show that, the proposed observer can estimate the transmission input&output shaft torque and wheel speed more effectively in different operating modes.

Development of Hybrid-Vehicle Energy-Consumption Model for Transportation Applications—Part I: Driving-Power Equation Development and Coefficient Calibration

This study is the first of a two-part paper. The overall study presents a new methodology to improve the accuracy of hybrid vehicles’ energy-consumption model over conventional transportation modeling methods. The first paper attempts to improve an equation for vehicles’ driving-power estimation to be more realistic and specific for a particular vehicle model or fleet. The second paper adopts the driving-power equation to estimate the requested driving power. Then, the data are utilized to construct the hybrid-vehicle energy-consumption model, namely, the traction-force–speed-based energy-consumption model (TFS model). The main concept of the first paper is to utilize the power-split hybrid powertrain’s accessible on-board diagnostics (OBD) dataset, and its dynamic model to estimate the total propulsion power. Then, propulsion power was applied as the main parameter for driving-power equation development and vehicle-specific coefficient calibration. For coefficient calibration, this study implemented the stepwise multiple regression method to select and calibrate an optimal set of coefficients. Results showed that conventional driving-power equations Vehicle-Specific Power (VSP) LDV 1999 and VSP Prius3Spec provide low prediction fidelity, especially under high-speed (>80 km/h) and heavy-load driving (≥50 kW). In contrast, D r v P w P r i u s 3 , proposed in this study, effectively improved prediction to become more accurate and reliable through all driving conditions and speed ranges. It dramatically helped to reduce prediction discrepancy over the conventional equations at heavy-load driving, from an R-square of 0.79 and 0.78 to 0.96. D r v P w P r i u s 3 also the prediction error at high-speed driving from the maximal error of approximately −20 to −5 kW. This study also discovered that aerodynamics and rolling resistance were the primary factors that caused the prediction error of conventional VSP equations. In addition, results in this study showed that both of the approaches used to establish the P P T d r v and D r v P w P r i u s 3 equations were valid for a power-split hybrid vehicle’s driving-power estimation. For the coefficient-calibration part, the stepwise and multiple regression method is low-cost and simple, allowing to calibrate an appropriate set of optimal coefficients for a specific vehicle model or fleet.

Model Predictive Control of Engine Start-up for Compound Power-split Hybrid Powertrain

Model Predictive Control of Engine Start-up for Compound Power-split Hybrid Powertrain

Integrated optimal design of configuration and parameter of multimode hybrid powertrain system with two planetary gears

The performance of power-split hybrid powertrain systems vary with its configuration due to the differences of the number of planetary gear (PG) set as well as the type, number and installation location of shift actuators (clutch or brake). The 2-PG scheme has some advantages over 1-PG and n-PG (n >=3) systems in terms of structure, performance, and control complexity of the system. The competitive advantages of 2-PG scheme depend on configuration design (analysis, evaluation and screening) and parameter optimization. In this article, systematic methods of configuration design, analysis, evaluation, and screening for 2-PG multimode power-split hybrid powertrain systems are proposed and all potential configurations of 2-PG, connection positions of power components, different number of actuators, and combinations of different operating modes have been taken into consideration. A stepwise optimization design method (DOE sampling with self-adaptive PSO algorithm) is also formulated to optimize the 2-PG system's characteristics parameters (the two ratios of ring gear to sun gear) and the ratio of main reducer. Finally, an efficient automatic development process and tool based on engineering constraints is designed to optimize the 2-PG system scheme and to achieve the excellent system performance.

Active damping of driveline vibration in power-split hybrid vehicles based on model reference control

The power-split hybrid vehicles are widely used owing to its advantages of high efficiency and low emission. With the increasing of the requirements of the customer’s satisfaction nowadays, vibration control is getting progressively more attention. Since the transmission system components are elastic to some extent, meantime the torque of the motor responds quickly for a sudden acceleration, hence torsional vibration takes place, henceforth the passengers will suffer inconvenience attributable to this vibration. This paper studies the active control algorithm for the torsional vibration of the power-split hybrid powertrains under rapid acceleration and deceleration circumstances. Primarily, a dynamic modeling of the power-split hybrid vehicle is built, in addition the uncertainty caused by the variable transmission ratio is analyzed. Moreover, this paper proposes a method combining the model reference adaptive control and the pole configuration method to solve the torsional vibration active control problem with uncertainties. The reference model is constructed by pole configuration method. Based on the dynamic characteristics of the reference model, the model reference adaptive control is implemented and the torque ripple reduction of output shaft under the impact conditions is achieved. Furthermore, this paper designs a dynamic coordinated control algorithm combined with active vibration control strategy, which ensures the dynamic performance and comfort performance of the vehicle. Finally, the effectiveness of this active vibration control strategy under cyclic conditions is verified using Simulink simulation and hardware-in-loop simulation.

Investigation of mode transition coordination for power-split hybrid vehicles using dynamic surface control

For passenger cars propelled by the dedicated compound power-split hybrid powertrain, driveline oscillations-induced vehicle jerks are often excited during clutch-to-clutch shift operations while drive mode changes. To tackle this issue, a coordinated dynamic surface control is developed by integrating clutch slips and motor torque compensation strategies through trajectories tracking of both clutch slip speed and wheel speed. Uncertainties or disturbances are treated to be additional inputs of the system, and model nonlinearities are considered and implemented in discretized form through lookup tables. A complex simulation model including electro-hydraulic system is proposed and validated via experiments. The coordinated controller is validated by collaborative simulation. Numerical examples are made and simulation results verify that the controller is effective and robust enough against parameters uncertainties.

Engine start-up optimal control for a compound power-split hybrid powertrain

Abstract Engine start-up is the key for the control of mode transition from electric drive mode to electronic-Continuously Variable Transmission (e-CVT) mode for a compound power-split hybrid electric vehicle (HEV). With the engine shaft directly connected to the powertrain through a torsional damper spring (TDS), the engine ripple torque (ERT) before ignition is amplified by the powertrain and transmitted to the wheel, which has a significant impact on the vehicle. To improve the ride comfort of the mode transition process, an engine start-up control strategy is proposed. First, the ERT model and the dynamic model of power-split powertrain were built, and the mode transition process was analyzed. Second, an optimal crank track of engine speed was designed based on the dynamic programming aiming at ride comfort. Third, the engine reference acceleration curve was calculated according to the optimal speed track, and an optimal engine start-up control strategy was proposed. Finally, through simulations of the dynamic programming the influence factors for engine start-up were examined, and the experiment results indicate that the proposed engine start-up optimal control can effectively improve the ride comfort during mode transition.

Optimal Design of Single-Mode Power-Split Hybrid Tracked Vehicles

Hybrid tracked vehicles are common in construction, agriculture, and military applications. Most use a series hybrid powertrain with large motors and operate at a relatively low efficiency. Although some researchers have proposed power-split powertrains, most of these would require an additional mechanism to achieve skid steering. To solve this problem and enhance drivability, a single-mode power-split hybrid powertrain for tracked vehicles with two outputs connected to the left and right tracks is proposed. The powertrain with three planetary gears (PGs) would then be able to control the torque on the two tracks independently and achieve skid steering. This powertrain has three degrees-of-freedom (DOF), allowing for control of the output torques and the engine speed independently from the vehicle running speed. All design candidates with three PGs are exhaustively searched by analyzing the dynamic characteristics and control to obtain the optimal design. Efficient topology design selection with parameter sizing and component sizing is accomplished using the enhanced progressive iteration approach to achieve better fuel economy using downsized components.

Novel Torsional Vibration Modeling and Assessment of a Power-Split Hybrid Electric Vehicle Equipped With a Dual-Mass Flywheel

The research described in this paper is aimed at exploring the effect of a dual-mass flywheel on the torsional vibration characteristics of a power-split hybrid powertrain. The dynamic equations of governing the torsional vibrations for this hybrid driveline are presented, a novel torsional vibration dynamic model is established with ADAMS, and the accuracy of this model is verified by using the mathematical model of the hybrid powertrain. Accordingly, various parameters of the dual-mass flywheel are investigated by using forced vibrations to reduce the torsional vibrations of the hybrid drive train. The analysis shows that the implementation of a dual-mass flywheel is an effective way to decrease the torsional vibrations of the hybrid powertrain. Finally, an improved combination of parameters yielding the least vibrations is provided.

Configuration optimization for improving fuel efficiency of power split hybrid powertrains with a single planetary gear

In order to significantly reduce vehicular fuel consumption and emission pollutants, power-split hybrid electric vehicles are increasingly deployed to ensure that internal combustion engines work at their high-efficiency regions. Because of multiple power components (internal combustion engine, two electric machines, and a driveshaft to the wheels), configurations of such vehicular powertrains are typically very complicated. In order to systematically analyze and design a fuel-optimal powertrain, an innovative hierarchical topological graph approach is proposed. This method comprises four major design processes: (1) modeling of hybrid vehicle powertrain systems, (2) generation of a configuration pool, (3) identification of isomorphism, and (4) classification of configuration modes. Potential power-split hybrid vehicle designs are rigorously examined via a dynamic programming algorithm to estimate their acceleration performance (0–100 km/h) and fuel economy in various driving cycles.

Investigation of a Novel Coaxial Power-Split Hybrid Powertrain for Mining Trucks

Due to the different working conditions and specification requirements of mining trucks when compared to commercial passenger vehicles, better fuel efficiency of mining trucks could lead to more significant economic benefits. Therefore, investigating a hybrid transmission system becomes essential. A coaxial power-split hybrid powertrain system for mining trucks is presented in this paper. The system is characterized as comprising an engine, a generator (MG1), a motor (MC2), two sets of planetary gears, and a clutch (CL1). There are six primary operation modes for the hybrid system including the electric motor mode, the engine mode, the hybrid electric mode, the hybrid and assist mode, the regenerative mode, and the stationary charging mode. The mathematical model of the coaxial power-split hybrid system is established according to the requirements of vehicle dynamic performance and fuel economy performance in a given driving cycle. A hybrid vehicle model based on a rule-based control strategy is established to evaluate the fuel economy. Compared with the Toyota Hybrid System (THS) and the conventional mechanical vehicle system using a diesel engine, the simulation results based on an enterprise project indicate that the proposed hybrid system can enhance the vehicle’s fuel economy by 8.21% and 22.45%, respectively, during the given mining driving cycle. The simulation results can be used as a reference to study the feasibility of the proposed coaxial hybrid system whose full potential needs to be further investigated by adopting non-causal control strategies.

Optimal design of power-split hybrid tracked vehicles using two planetary gears

Power-split hybrid powertrains have been thus far successfully used for production passenger cars and SUVs but not for tracked vehicles. For example, track-type dozer (TTD) models available on the market tend to use series hybrid powertrains, which frequently require a separate steering mechanism, resulting in lower operating efficiency. Looking to the future, power-split hybrid technologies have high potential for tracked vehicles to circumvent the limitation. This paper proposes a design process for multi-mode power-split powertrains for TTDs. The powertrain is designed to achieve separate control of two sides of tracks to enable skid steering. To systematically search for all possible designs with two planetary gears, an optimal methodology is proposed. An automated modelling process is proposed to obtain the dynamic equations efficiently. A near-optimal energy management strategy is used to achieve near-optimal fuel economy. The approach successfully identifies two designs that achieve better overall performance compared with the benchmark.

Usage-based optimisation of characteristic maps for conceptual powertrain design

With an increasing number of vehicles having alternative powertrains, the choice of the most appropriate powertrain for a vehicle class or load cycle is more challenging. This paper introduces a method for usage-based optimisation of powertrains. Based on a longitudinal dynamic simulation, the characteristic maps of the traction machines are optimised for different user cycles and these characteristic maps form the objective function of a minimisation problem. The goal of optimisation is to minimise well-to-wheel carbon dioxide emissions. Besides the conventional powertrain provided with petrol or diesel engine, battery electric, parallel-, serial- and power-split hybrid powertrains with assisting or dominating petrol and diesel engines are investigated. The results show that the proposed method delivers the optimal powertrain for a specific usage by applying an optimisation with reasonable restrictions.