Hybrid Electric Vehicle Transmissions Research Articles

Parameter Optimization and Control Strategy of Hybrid Electric Vehicle Transmission System based on Improved GA Algorithm

Most of the traditional hybrid electric vehicles (HEVs) choose to optimize the transmission ratio parameters, and the parameter changes of the whole vehicle and other components are only calculated as fixed values. It is difficult to give consideration to the optimization of the economy and power of hybrid vehicles. Therefore, the research proposes to build the transmission ratio, the required power of the vehicle’s working mode, and other models through the dynamic analysis. The parameters of the whole vehicle are optimized on the basis of parameter matching. At the same time, this paper chooses to adopt a hybrid optimization algorithm, combining particle swarm optimization (PSO) and genetic algorithm (GA). The weighted average method and constraint method are used to design the fitness function. The simulation experiment is carried out by Cruise software and MATLAB. Compare the iterative fitness of the PSO-GA algorithm with the traditional PSO and GA algorithm. It can be concluded that PSO-GA converges at the 12th iteration, with an average optimal fitness of 0.5239, which is higher than the traditional algorithm. At the same time, the parameter optimization of PSO-GA and the simulated annealing algorithm is compared. It is found that in the same task, the gasoline consumption after SA algorithm optimization is 0.561 L, while the fuel consumption under PSO-GA algorithm optimization is 0.475 L. The method proposed in this study has improved the power and economy of the HEV model and is effective.

Generation and Analysis of Hybrid-Electric Vehicle Transmission Shift Schedules with a Torque Split Algorithm

The increased concern over global climate change and lack of long-term sustainability of fossil fuels in the projected future has prompted further research into advanced alternative fuel vehicles to reduce vehicle emissions and fuel consumption. One of the primary advanced vehicle research areas involves electrification and hybridization of vehicles. As hybrid-electric vehicle technology has advanced, so has the need for more innovative control schemes for hybrid vehicles, including the development and optimization of hybrid powertrain transmission shift schedules. The hybrid shift schedule works in tandem with a cost function-based torque split algorithm that dynamically determines the optimal torque command for the electric motor and engine. The focus of this work is to develop and analyze the benefits and limitations of two different shift schedules for a position-3 (P3) parallel hybrid-electric vehicle. a traditional two-parameter shift schedule that operates as a function of vehicle accelerator position and vehicle speed (state of charge (SOC) independent shift schedule), and a three-parameter shift schedule that also adapts to fluctuations in the state of charge of the high voltage batteries (SOC dependent shift schedule). The shift schedules were generated using an exhaustive search coupled with a fitness function to evaluate all possible vehicle operating points. The generated shift schedules were then tested in the software-in-the-loop (SIL) environment and the vehicle-in-the-loop (VIL) environment and compared to each other, as well as to the stock 8L45 8-speed transmission shift schedule. The results show that both generated shift schedules improved upon the stock transmission shift schedule used in the hybrid powertrain comparing component efficiency, vehicle efficiency, engine fuel economy, and vehicle fuel economy.

Development Trends of Transmissions for Hybrid Electric Vehicles Using an Optimized Energy Management Strategy

Energy conservation and emissions reduction have become increasingly significant for automobiles due to the severity of the current energy situation. Hybrid electric vehicle (HEV) technology is one of the most promising solutions. This study investigated the total efficiency of a HEV powertrain. To improve the total efficiency, the engine should be regulated to work at its highest efficiency and drive the wheels directly as much as possible. To accomplish this, we developed an energy management strategy based on the direct drive area (DDA) of the engine’s efficiency map. Several typical HEV models were built to compare the fuel consumption using DDA and rule-based strategies. Furthermore, the function of the HEV transmission system with DDA was considered. The transmission in a HEV should regulate the engine to work at its highest efficiency as much as possible, which is rather different than the regulation in an internal combustion engine vehicle. The functional change may lead to transmission systems with fewer gears but optimal gear ratios. If this trend is realized, the manufacturing cost of HEVs could be largely reduced.

Research on Gear-Shift Strategy without Disengaging the Clutch for Automated Manual Transmission in Hybrid Electric Vehicle

In order to realize a quick, smooth and precise shifting process of hybrid electric vehicle (HEV) equipped automated manual transmission (AMT), a research platform for HEV driven by electrically controlled engine and drive motor was established. The key technologies including its system components, working principle, control strategy of engine and motor during shifting process were analyzed. A technology of AMT shift without disengaging the clutch was proposed. According to the dynamic characteristics of the HEV’s engine, motor, and transmission, the dynamic model of transmission system was established. The various stages of shifting process were emphatically analyzed. Its shift characteristics and the key factors affecting the shift quality were grasped. On the basis of the above researches, the shift control strategy without disengaging the clutch was acquired. It was verified on a demo HEV platform. The results showed that the technology of AMT shift without disengaging the clutch for HEV not only ensured smooth shifting through the coordinated control of engine, motor and actuator, but also shortened the shift time and improved the shift quality significantly.

Downshift decision and process optimal control of dual clutch transmission for hybrid electric vehicles under rapid braking condition

Abstract Hybrid electric vehicles (HEVs) equipped with dual clutch transmission (DCT) can benefit from engine auxiliary braking force and driving motor regenerative braking force in braking conditions. This can effectively reduce the workload of hydraulic mechanical braking systems and recovery braking energy, which will improve the fuel economy. In the downshift process, the driving motor is involved to response the change of torque/speed demand, which can further improve the shift quality of DCT without affecting the engine emissions and fuel economy. The combined braking condition of HEVs with DCT allows for the variation of power distribution between the front and rear axle, as well as the electric and hydraulic braking force. In this study, the downshift decision strategy is designed based on the two-parameter shift schedule, while considering the driver’s subjective driving intention. Subsequently, the mathematical model developed to investigate the downshift process of HEVs with dual clutch transmission has been applied to skip downshift process, to analyze the control sequence and implement different control algorithms according to respective control objects. Specifically, the sliding mode variable structure optimization control algorithm is used to allow the engine speed to track the target value in the torque phase. In addition, the linear quadratic tracking controller and the model reference adaptive system are used, based on adjustable parameters, to realize the speed synchronization of the clutch driving and driven plate in the inertial phase. According to the results of electro-hydraulic braking force distribution, the braking forces of an integrated starter generator (ISG) motor and hydraulic brake system are controlled to switch to the demand level. Then, the simulation model established on a Matlab/Simulink platform is used to validate the skip downshift control strategy. Finally, the designed control strategies are verified on the test bench. The test results demonstrate that the established shift control strategy can achieve the target power downshift under braking conditions, and have a good downshift quality, which lays a foundation for subsequent development and real vehicle tests.

Design Optimization of an Electric Variable Transmission for Hybrid Electric Vehicles

An electric variable transmission (EVT) for hybrid electric vehicles (HEVs) is investigated in this paper. With a special double rotor structure, the EVT splits and reintegrates the output power of the internal combustion engine (ICE) to run at its optimum working efficiency. However, the high electromagnetic coupling degree causes torque ripple and affects the dynamic performance of the EVT. After introducing the configuration and working principle, the torque mathematical model of the EVT in an ABC three-phase coordinate system is proposed to analyze the cause of this torque ripple. Besides, a finite element method-based (FEM) structural optimization design for reducing the torque ripple and improving the working stability is presented. The magnetic field distribution, induced voltage and torque property validate the rationality of optimization.

Rapid optimal design of a multimode power split hybrid electric vehicle transmission

This work aims at presenting a design methodology capable of modeling, generating, and testing a large number of multimode power split hybrid electric vehicle transmission designs in a relatively short period of time. Design parameters include the planetary gear ratios, the final drive ratio, the configuration of hookups to link the hybrid powertrain components to the planetary gear sets and the locations of clutch connections between different nodes of the planetary gear sets. The system modeling approach is first presented, including formulations for each component (the vehicle and road load, the engine, the motor/generators and the battery). A rapid and automated modeling procedure is proposed for hybrid electric vehicle transmissions including multiple planetary gear sets and clutch connections. Two algorithms are subsequently presented that enable fast evaluation of fuel economy and acceleration performance of hybrid electric vehicle transmission designs, namely the enhanced Power-Weighted Efficiency Analysis for Rapid Sizing and the Rapid Efficiency-based Launching Performance Analysis algorithms. The developed design methodology is tested by first modeling and evaluating three hybrid electric vehicle designs from the state-of-art. Later, an investigation for optimal designs that can ameliorate the examined benchmarks is performed. Several millions of design options are rapidly generated and tested using the proposed procedure. The methodology is proved effective by quickly coming up with two sub-optimal designs. Fuel economy and acceleration performance are improved by 5.56% and 40.56%, respectively, compared to the corresponding best benchmarks.

Economic MPC-based transient control for a dual-mode power-split HEV

The existing research into hybrid electric vehicle (HEV) control is mainly focussed on the optimisation of the power distribution between a conventional internal combustion engine (ICE) and an alternative power source (usually a battery pack), however, transient control, which is a key technique that affects both fuel economy and the drivability of the HEV, has not been fully addressed. Especially in dual-mode power-split HEVs, due to the different dynamic characteristics of the actuators in the transmission, and its complicated speed-torque relationship, transient control also affects the precision of power distribution and the speed of response of the electric output power. To improve the transient control performance, the design of an economic model predictive control (EMPC)-based transient controller for a dual-mode power-split HEV is developed. By incorporating an experimental identification model of a diesel ICE in a control-oriented transmission model, a better coordination among the actuators involved in HEV transmission can be achieved. Moreover, an ICE efficiency index is also added to the objective function to improve ICE fuel efficiency during this transient process. Then, a fast MPC method is applied to reduce the on-line computation effort required of the proposed control algorithm. By the flexible application of the EMPC and an innovative ICE model which is suited to the control-oriented model in EMPC, the transient control performance was improved. The effectiveness, and the real-time performance, of the control algorithm are validated by way of MATLAB™/Simulink-based simulations, as well as test-bed experiments combined with the use of the RapidECU platform.

Design and simulations of dual clutch transmission for hybrid electric vehicles

Dual clutch transmissions (DCTs) refer to the double friction clutches; they are designed and operated fully automated in vehicle shift gearbox. The biggest advantage of the DCTs is the improvement of the fuel economy because the power flow from the engine to the transmission is always has a very high friction coefficient and is not interrupted. The current six-speed DCTs can provide more than 10% better fuel economy compared to the conventional six-speed automatic gearbox. This paper develops three vehicle models: conventional dual clutch transmission (DCT); conventional hybrid electric vehicle (HEV); hybrid dual clutch transition (HDCT). They are simulated on different drive-cycles. HEV and HDCT proved the superiority on fuel savings in low speeds. HDCT shows a little bit higher energy saving over HEV due to the higher efficiency of clutches to torque converters. Conclusions and recommendations for the development of DCT, HEV, and HDCT are also outlined.

Design and simulations of dual clutch transmission for hybrid electric vehicles

Dual clutch transmissions (DCTs) refer to the double friction clutches; they are designed and operated fully automated in vehicle shift gearbox. The biggest advantage of the DCTs is the improvement of the fuel economy because the power flow from the engine to the transmission is always has a very high friction coefficient and is not interrupted. The current six-speed DCTs can provide more than 10% better fuel economy compared to the conventional six-speed automatic gearbox. This paper develops three vehicle models: conventional dual clutch transmission (DCT); conventional hybrid electric vehicle (HEV); hybrid dual clutch transition (HDCT). They are simulated on different drive-cycles. HEV and HDCT proved the superiority on fuel savings in low speeds. HDCT shows a little bit higher energy saving over HEV due to the higher efficiency of clutches to torque converters. Conclusions and recommendations for the development of DCT, HEV, and HDCT are also outlined.

Configuration synthesis of series–parallel hybrid transmissions

The purpose of this paper is to synthesize systematically the feasible configurations of series–parallel hybrid transmissions for automotive systems utilized in passenger vehicles subject to the deduced design constraints. The design process includes the following steps: first, search for all feasible mechanisms that can be used for synthesizing hybrid transmissions; second, identify all potential locations for the inputs and the output to the mechanisms; third, identify all potential locations for clutches and the brakes of the systems subject to the required operation modes. Through the proposed design process, 30 planetary gear trains for hybrid electric vehicle transmissions with seven members and 10 joints are generated. The power arrangement process generates 42 clutchless hybrid systems. Then, the clutch arrangement process generates 48 corresponding series–parallel transmissions. To demonstrate the feasibility of the synthesized configurations, a novel configuration system is taken as a numerical example to illustrate the principles of operation and performance.

Double-Rotor Switched Reluctance Machine (DRSRM)

With the era of modern vehicle electrification, electric machines with high traction torque–speed output and compact volume are highly desired. This paper presents a family of switched reluctance machine configurations that are composed of double rotors and one stator integrated in one machine housing. The machines are potentially more compact and lower cost, while providing two independent mechanical outputs suitable for hybrid electric vehicle transmissions. The detailed design process of a double-rotor switched reluctance machine (DRSRM) is presented, comprising of analytical calculations, finite-element field analysis, and full-drive system simulation. Additionally, some optimizations are applied to maximize the machine performance and minimize the machine weight and volume. A scaled prototype machine is designed and built according to chosen vehicle drive cycles to evaluate and validate the DRSRM prototype.

Field Weakening Control of a PM Electric Variable Transmission for HEV

This paper presents the control of a Permanent Magnet Electric Variable Transmission (PM-EVT) for Hybrid Electric Vehicles (HEVs). Consisting of two electric machines, the EVT realizes the power split function in an electromagnetic way rather than in a mechanical way. A specific PM-EVT has been designed for Toyota Prius II. The control scheme of the entire vehicle is deduced using the Energetic Macroscopic Representation methodology. The energy management strategy yields local control references. A specific attention is paid for the field weakening for wide speed range. Simulation results are provided to illustrate the EVT modeling and control.

Analysis of circulating power within hybrid electric vehicle transmissions

Since multiple paths of power flow exist in many transmissions, an undesirable situation of power circulation can arise in the system which leads to high mesh losses and less overall efficiency of the system. The paper presents a detailed analysis of circulating power within a planetary gear transmission used for hybrid vehicles. The fundamental relations connecting torques, speeds and power flows for a general planetary drive mechanism, are derived from the first principles for kinematic and power flow analysis. The power flow relations are investigated and clearly defined for the analysis of circulating power within complex chains of planetary drives and they also permit an immediate derivation of the power flow in all inversions of planetary drives. This study contributes to the development of a methodology for the circulating power-flow analysis of a planetary gear drive with two inputs and one output. This approach is generic and an illustration is presented to demonstrate its applicability to a hybrid planetary gear configuration. It is found that circulating power depends on planetary gear ratios and speed ratio of two power sources.

A control-oriented simulation model of a power-split hybrid electric vehicle

A simulation model of a two mode power-split hybrid electric vehicle (HEV) is proposed in this paper for the purpose of HEV dynamics analysis and control system design. The bond graph methodology is used to model dominant dynamic effects of the mechanical part of the HEV transmission. Simple quasi-static battery model, the environment model, the tire and the power losses model of a vehicle are included, as well. A low-level electric generator speed control loop is designed, which includes a PI controller tuned according to the symmetrical optimum tuning procedure. Finally, off-line optimization by conjugate gradient-based BPTT-like optimal control algorithm, which is based on the presented mathematical model, is also given in the paper.

Bond graph modelling and power flow analysis of series-parallel HEV transmissions

The bond graph method is used to model kinematics and dynamics of various one-mode and two-mode series–parallel configurations of Hybrid Electric Vehicle (HEV) transmissions. The bond graph method is also used to analyse the power flow of the considered transmissions in electric variator and full-hybrid operating modes. The analysis is illustrated by numerical static curves related to the maximum transmission output torque for a wide range of vehicle velocities.

Bond Graph Modeling of Automotive Transmissions and Drivelines

AbstractThe paper presents an overview of the bond graph models of advanced automotive transmission and driveline systems. This includes one-mode and two-mode series-parallel hybrid electric vehicle transmissions, a continuous variable transmission, active-limited slip and torque vectoring differentials in 2WD and 4WD configurations, and electromechanical actuator-based wet and dry clutch actuation systems. It is illustrated that the bond graph method can be effectively used to gain valuable insights about the system dynamics structure and behavior.

A Hybrid Electric Vehicle Transmission Chain Simulator Based on Electromechanical Actuators

This paper presents a hybrid electric vehicle transmission chain simulator connected to longitudinal vehicle motion. The transmission simulator uses electric actuators to reproduce the mechanical characteristics of a real vehicle engine and its transmission chain. The developed approach allows to validate transmission and vehicle dynamic studies (control of automatic or robotized gearboxes, test of heat engine, dynamic behavior and passenger comfort...) without need to the real transmission system and the real environment of the vehicle. The proposed system is used to carry out a vehicle automated driving for a cruise control test. The control law strategy consists on a first sliding mode. The performances of the controller are presented to demonstrate the effectiveness of the proposed approach.

Control strategy for a dual-mode electromechanical, infinitely variable transmission for hybrid electric vehicles

An operating strategy is proposed for a dual-mode electromechanical, infinitely variable transmission (EVT) hybrid electric vehicle (HEV). First, network analysis is performed to evaluate the dual-mode EVT efficiency with respect to the speed ratio. It is found from the network analysis that the EVT efficiency decreases when the power circulation occurs along the electric variator and the EVT should be operated in the speed ratio region that provides a relatively high system efficiency, which requires an operating strategy from the viewpoint of the overall powertrain efficiency rather than the internal combustion engine thermal efficiency. In order to develop the operating strategy of the dual-mode EVT, dynamic equations of the HEV powertrain including the EVT are obtained and the motor torque control algorithm is designed using inversion-based control. To evaluate the performance of the operating strategy, an HEV simulator is developed on the basis of the dynamic models of the HEV powertrain using Cruise and MATLAB/Simulink. The simulation results indicate that the operating strategy proposed in this study is able to operate the engine in the desired speed ratio range having a relatively high EVT efficiency, which provides improved fuel economy compared with conventional control. It is expected that the operating strategy based on the transmission efficiency can be used effectively in the design of the dual-mode EVT for HEV application.

Circulating mechanical power in a power-split hybrid electric vehicle transmission

Recently, a new power-split hybrid electric vehicle drivetrain has been developed by the Corporate Research and Development Department of the Robert Bosch company and two research cars equipped with this powertrain have been built. Owing to the loop-like arrangement of the shafts in the newly developed Dual-E Transmission, circulating power can arise in this system. In general, circulating power leads to high mesh losses because the power transmitted by some components becomes greater than the input or output power. This paper presents a detailed analysis of circulating power in the Dual-E Transmission. It is shown that the solution of the energy balance equations is given by a linear combination of four basic power flows. The factors in this linear combination, however, cannot be uniquely determined from the energy balance alone. Therefore, the transmission kinematics and dynamics are dealt with in detail. Subsequently, a mathematical description as well as a graphical representation of the circulating-power-free operating range are derived. This elaboration provides a solid basis for the development of a fuel-efficient operating strategy.