Electrical Continuously Variable Transmission Research Articles

An improved time-varying mesh stiffness calculation method and dynamic characteristic analysis for helical gears under variable torque conditions

Based on the slice theory and numerical calculation methods, the time varying meshing stiffness (TVMS) calculation method of the gear pair was constructed for the helical gear pair of a electric continuously variable transmission (ECVT), and the TVMS of the helical gear were calculated under different constant and time-varying torque in this study. The obtained stiffness values were introduced into the established dynamics model of helical gear system, and the influence of changed TVMS, resulting from the variable speed and torque, on the nonlinear dynamic characteristics of gear pair was analyzed using the Runge-Kutta method. The results show that the proposed TVMS calculation method is very effective in computing the TVMS of helical gear pair under time-varying condition. The TVMS and dynamic transmission error (DTE) increase as the torque increase, and vice versa. Meanwhile, the system exhibits a diverse range of periodic, sub-harmonic, and chaotic behaviors at high speed and at low speed when torque is low, whereas not appear at steady high torque under low speed range. This study offers a method for gaining the TVMS of helical gear pair to analyze the dynamic characteristics of gear pair under actual working condition, and the influence of torque that change with the speed ratio on the dynamic performance of a gear system should be considered in the industrial applications.

A Quasi-Sinusoidal Concentrated Winding Used in an Integrated Magnetic-Field-Modulated Brushless Compound-Structure Machine

As a promising candidate of the electrical continuously variable transmission (ECVT), the integrated magnetic-field-modulated brushless compound-structure machine (IMFM-BCSM) has advantages of compact structure and no brush. The IMFM-BCSM is composed of a stator with two sets of windings, a permanent-magnet (PM) rotor and a modulation rotor. Due to its special operating principle, i.e., the magnetic field modulation principle, the back electromotive force (EMF) waveform distortion of the IMFM-BCSM is more serious than that of the conventional PM machine. To solve the above problem, a quasi-sinusoidal concentrated winding (QSCW) configuration is proposed and corresponding design method is further introduced. In order to observe the filtering ability of the QSCW, comparisons between QSCW configuration and fractional-slot concentrated winding configuration are carried out. The results show that when the QSCW configuration is employed, the no-load back EMF of the regular winding is more sinusoidal; the distortion degree is less affected by the rotor speeds; and the torque ripple is much smaller. Finally, a prototype is manufactured to verify the theoretical analysis.

Design of Gerotor Pump and Influence on Oil Supply System for Hybrid Transmission

Electric continuously variable transmission (E-CVT) is a vital part of the automobile in order to enhance the power coupling. The oil pump is an important power source component in the hybrid transmission system. Its efficiency exerts a significant impact on the efficiency of the oil supply system and even the hybrid transmission system. In this study, a gerotor pump is designed in line with the requirements of a certain type of hybrid electric vehicle. A Non-dominated Sorting Genetic Algorithm II (NSGA-II) genetic algorithm was employed to optimize the rotor tooth profile. The proportional-derivative (PD) control of the oil supply system was realized to lower the functional error of the oil supply system based on the AMESim simulation platform. In addition, the prototype test was performed to verify the rationality of the design.

Optimized design and performance analysis of a magnetic-field modulated brushless dual-mechanical port motor with Halbach array permanent magnets

In order to develop an electrical continuously variable transmission (E-CVT) to replace mechanical power coupling equipment applied in series-parallel hybrid electric vehicle (HEV), this paper proposes a magnetic-field modulated brushless dual-mechanical port motor with Halbach array permanent magnets, which has a more compact structure. The operating characteristics are analyzed by the lever analogy. It is concluded that the motor can realize the speed and torque decoupling between the engine and the wheel, which meet multi-mode operation requirements for HEV. To realize the multi-objective design of torque output, torque ripple and usage amount of permanent magnets, an optimization scheme combined parameter sensitivity with response surface methodology is adopted. The trade-offs among the optimization objectives are considered, then the key structural parameters and its optimal values are efficiently determined. Based on a two-dimensional model, the electromagnetic performances are simulated and analyzed. The results show that, after the parameters optimization, the no-load back electromotive force (EMF) has better sinusoidal characteristic, and the torque ripples and cogging torque peaks of the motor have been significantly reduced. Furthermore, a prototype motor is tested. The experimental results are consistent with the simulation results, which demonstrates the validity of the proposed structure and parameter optimization method.

Optimal sizing and adaptive energy management of a novel four-wheel-drive hybrid powertrain

Hybrid powertrain technology must be applied to sport utility vehicles (SUVs) to meet stringent fuel economy and emissions standards. As an essential attribute of SUV, four-wheel-drive (4WD) offers flexible torque arrangement and results in safe and powerful driving under off-road conditions. In this paper, we propose a novel compound 4WD hybrid powertrain by adding an extra output shaft to a conventional power-split hybrid electric vehicle. By connecting two output shafts to the front and rear axles, this hybrid powertrain could deliver the engine power to four wheels simultaneously, while maintaining the electrical continuously variable transmission (ECVT) function. The dynamics, modeling and system characteristics of the compound 4WD hybrid powertrain are presented firstly. Using an integrated optimization framework to optimize components’ sizes, the proposed 4WD hybrid powertrain indicates 36.22% and 13.82% fuel economy improvements than conventional 4WD SUV in city and highway cycles, respectively. Since it is difficult to implement the DP in real-time controller, we present an adaptive equivalent consumption minimization strategy (A-ECMS), whose equivalent factor (EF) is constrained by its theoretical extremum. Finally, simulation results show A-ECMS achieves better fuel economy than regular ECMS.

Differential Evolution-Based Multiobjective Optimization of the Electrical Continuously Variable Transmission System

With the increasing popularity of hybrid electric vehicles (HEVs), the demands of improving the fuel economy and energy efficiency of HEVs are enlarged. The technology electrical continuously variable transmission (E-CVT) system provides the opportunity to fulfill this requirement. However, conventional E-CVT with planetary gears suffer from frictional loss, high maintenance, and audible noise. Therefore, a series of gearless E-CVT propulsion systems are developed. Thereinto, a double-rotor single-stator brushless E-CVT having high torque density, reduced stator end winding length, and reduced copper loss was recently proposed. However, only torque of the E-CVT system is optimized by the genetic algorithm in the previous study. This paper adopts a differential evolution algorithm coupled with finite element method to optimize torque, energy efficiency, torque ripples, and multiobjective of the E-CVT system by reconfiguring the height of rotors, the areas of slots, and the height of yoke. It is simulated that by only tuning the weighting factors, the permanent magnetic machine in the E-CVT system can operate in the highest torque mode, highest energy efficiency mode, lowest torque ripples mode, and multiobjective optimization mode.

A Study on Magnetic Decoupling of Compound-Structure Permanent-Magnet Motor for HEVs Application

The compound-structure permanent-magnet (CSPM) motor is used for an electrical continuously-variable transmission (E-CVT) in a hybrid electric vehicle (HEV). It can make the internal combustion engine (ICE) independent of the road loads and run in the high efficiency area to improve the fuel economy and reduce the emissions. This paper studies the magnetic coupling of a new type of CSPM motor used in HEVs. Firstly, through the analysis of the parameter matching with CSPM in the HEV, we receive the same dynamic properties’ design parameters between the CSPM motor and the THS (Toyota Hybrid System) of the Toyota Prius. Next, we establish the equivalent magnetic circuit model of the overall and the secondary model considering the tangential and radial flux distribution in the outer rotor of the CSPM motor. Based on these two models, we explore the internal magnetic coupling rule of the CSPM motor. Finally, finite element method analysis in 2D-ansoft is used to analyze the magnetic field distribution of the CSPM motor in different operation modes. By the result of the finite element method analysis, the internal magnetic decoupling scheme is put forward, laying the theoretical foundation for the further application of the CSPM motor in HEVs.

Investigation of a Magnetic-Field Modulated Brushless Double-Rotor Machine With the Same Polarity of PM Rotor

Owing to getting rid of brushes and slip rings, the magnetic-field modulated brushless double-rotor machine (MFM-BDRM) can be a promising candidate for the electrical-continuously variable transmission (e-CVT) in hybrid electric vehicles (HEVs). However, since there are many magnetic-field harmonics with the high rotating speed in the air gap, the PM loss is a big problem in traditional MFM-BDRMs [1]. Therefore, a new MFM-BDRM with the same polarity of PM rotor is proposed, which has advantages of reducing PM loss, saving PM material and keeping good electromagnetic performance. The magnetic field distribution in the air gap, the back electromagnetic force (EMF) and torque performance of the proposed MFM-BDRM are investigated. To obtain the optimum design scheme, the influence of PM pole-arc coefficient on the torque performance is investigated. Then the torque performance is further optimized by the span ratio of magnetic blocks. To evaluate the overall performance of this new MFM-BDRM, a traditional MFM-BDRM with the same size is designed to compare their performances.

Design Optimization of a Novel Doubly Fed Dual-Rotor Flux-Modulated Machine for Hybrid Electric Vehicles

The doubly fed dual-rotor flux-modulated (DFDRFM) machine is a promising electrical continuously variable transmission (E-CVT) concept for the hybrid electric vehicles as it has two mechanical ports and two electrical ports, which are highly desirable for E-CVT. In this paper, a novel DFDRFM machine is proposed. Compared with previous designs, the most prominent merits are its compactness and robustness. In addition, it is easy to manufacture. After introducing its structure and working principle, the influence of dimensions on its torque and loss is analyzed. A genetic algorithm and finite-element method-based design optimization method, which aims to increase the efficiency of the proposed machine, is presented.

Novel Electrical Continuously Variable Transmission System and its Numerical Model

A novel electrical continuously variable transmission (E-CVT) system for hybrid electric vehicles is presented. The merits of the system, which is comprised of a magnetic gear (MG) integrated permanent magnet brushless machine, are its compactness, light weight, very high torque density, and simple structure. The integrated MG is ingeniously used to greatly amplify its output torque. It serves the functions of both power splitting and coupling. The drawbacks of mechanical gears or brushes in traditional systems are overcome. A design method based on finite element method for maximizing the torque output of the machine is presented and the performance of the machine in the E-CVT system is validated.

A Novel Double-Stator Double-Rotor Brushless Electrical Continuously Variable Transmission System

A novel double-stator, double-rotor brushless electrical continuously variable transmission (E-CVT) system is proposed. This machine incorporates an inner stator which can fully utilize the space inside the inner rotor so as to reduce the volume of the machine. This design is based on magnetic flux modulating and magnetic gear effect to make the E-CVT system work in different operating modes. Different control modes of this proposed machine are also discussed and analyzed, including pure electric mode, hybrid mode, and battery charging mode. Time-stepping finite element method (TS-FEM) is used to analyze the dynamic performance of the machine. TS-FEM simulation results are reported to verify the validity of the proposed design.

Design of a Novel Electrical Continuously Variable Transmission System Based on Harmonic Spectra Analysis of Magnetic Field

A novel electrical continuously variable transmission (E-CVT) system is presented and analyzed based on harmonic spectra analysis of magnetic fields. Two rotors and one stator are integrated within one electric machine so as to keep the whole system compact. The main merits of this proposed torque transmission machine are its brushless structure, improved torque density, reduced stator end winding length, and reduced copper loss. The operating principle of the machine is described and its steady-state and transient performances are analyzed using time-stepping finite element method (TS-FEM). FEM results are used to confirm and validate the superior performance of the proposed machine.