Fractional slot concentrated winding (FSCW) permanent magnet synchronous machines (PMSMs) have been a research hotspot over the past few decades. Recently, the magnetic gearing effect in FSCW PMSMs ...is revealed along with its gear ratio, which is a function of slot/pole number combination. At the design stage of FSCW PMSMs, one of the key issues is the selection of the slot/pole number combination. This paper shows that the gear ratio can contribute to a proper slot/pole number selection in any multiphase FSCW PMSMs by acting as a unified index for a quick overall performance comparison. In this paper, first, the magnetic gearing effect in FSCW PMSMs is explained and the gear ratio is further discussed. The advantages of adopting gear ratio as the overall performance index over other indices are revealed. The influence of the gear ratio on the winding factor, torque output, cogging torque, inductance, and rotor losses of three- and six-phase FSCW PMSMs is analyzed and validated by experiments, thus proving the analyses.
•Developing an EV model including two-motor and two-speed powertrain system.•Effect analysis of gear ratios and torque distribution on the driving requirements.•Formulating an multi-objective ...optimization problem for efficiency and performance.•Constructing the surrogate models using an effective adaptive sampling method.•Obtaining the Pareto solutions including optimal gear ratios and torque distribution.
In an electric vehicle (EV), a two-motor and two-speed powertrain system is superior to other powertrain systems in terms of the driving requirements, achieving an excellent dynamic performance and energy efficiency. Because the most important design specifications for a two-motor and two-speed powertrain are the motor torque distribution between the two motors, and the first and second gear ratios, these specifications should be optimized to improve both performance and efficiency as much as possible. To analyze such requirements, an EV model, including two-motor and two-speed powertrain system, was constructed. The acceleration time and energy consumption were employed as the evaluation criteria for the quantification of performance and efficiency, respectively, and the analysis results when changing the gear ratios and the torque distribution, show that these specifications significantly influence on the performance and efficiency. Therefore, an optimization of gear ratios and torque distribution is essential for achieving a superior powertrain system of an EV. Because of the trade-off relationship between the performance and efficiency, a multi-objective optimization problem is formulated to minimize the acceleration time and energy consumption. To decrease the excessive computational effort during a multi-objective optimization process, efficient surrogate models of each objective function were developed using an artificial neural network and an adaptive sampling method. The surrogate model-based optimization was performed, and the optimization results show a Pareto front that provides a variety of optimal solutions between the objective functions, as well as the validity of the surrogate model-based multi-objective optimization.
Attainable gear quality is a crucial criterion for the broad industrial application of the gear roll-forming process. One of the main defects in gear rolling process is the rabbit ear, which affects ...the effective tooth depth of the formed workpiece and the material utilization rate. To further understand the influencing factors of rabbit ear, this paper proposes analytical models of relative sliding distance and frictional shear stress to explain the material flow on the tooth flank of the workpiece. The influence of rolling parameters (rotational speed of rolling tools, lubrication, rotational direction of rolling tools), number of workpiece teeth, and positive addendum modified rolling tools on rabbit ear was studied theoretically based on the established models and a case study. Finally, experimental results were displayed to verify the above-mentioned analysis. The results reveal that better lubrication, higher rotational speed, and reverse rotation of rolling tools contribute to weakening the rabbit ear effect. Moreover, the rabbit ear height in case of
z
2
= 70 decreases by 14.2% compared to that in case of
z
2
= 46 due to reduced gear ratio. Additionally, rabbit ear height formed by rolling tools with a positive addendum modification coefficient of 1.0 amounts to approximately 48.3% of that generated by rolling tools having standard teeth in the gear forced throughfeed rolling process.
Flux-modulated-type magnetic gears are expected to be applied as a step-up gear for wind-power generation because of their advantages, including high torque density and maintenance-free operation. ...Furthermore, the flux-modulated-type magnetic gears with an axial-flux structure have attracted great attention recently since they have a smaller axial length and are relatively easy to assemble. In some cases, magnetic gears are required to have an integer gear ratio based on the design requirements of the entire system, which results in larger cogging torque in the high-speed (H-speed) rotor that causes vibration, acoustic noise, and startup error. A skewed rotor structure is well known to be capable of reducing the cogging torque; however, it is complicated and poor in assembling, especially in a large-scale axial-flux magnetic gear (AFMG) used for the wind-power generation. To resolve the above problem, this article presents two new types of pole pieces for reducing the cogging torque: one is an unequal-space type, and the other is an unequal-width type. The validity of the two newly proposed types of pole pieces is proved by both a 3-D finite-element method (3D-FEM) and experiment.
According to the force-length-velocity relationships, the muscle force potential is determined by the operating length and velocity, which affects the energetic cost of contraction. During running, ...the human soleus muscle produces mechanical work through active shortening and provides the majority of propulsion. The trade-off between work production and alterations of the force-length and force-velocity potentials (i.e. fraction of maximum force according to the force-length-velocity curves) might mediate the energetic cost of running. By mapping the operating length and velocity of the soleus fascicles onto the experimentally assessed force-length and force-velocity curves, we investigated the association between the energetic cost and the force-length-velocity potentials during running. The fascicles operated close to optimal length (0.90 ± 0.10
) with moderate velocity (0.118 ± 0.039
maximum shortening velocity) and, thus, with a force-length potential of 0.92 ± 0.07 and a force-velocity potential of 0.63 ± 0.09. The overall force-length-velocity potential was inversely related (
= -0.52,
= 0.02) to the energetic cost, mainly determined by a reduced shortening velocity. Lower shortening velocity was largely explained (
< 0.001,
= 0.928) by greater tendon gearing, shorter Achilles tendon lever arm, greater muscle belly gearing and smaller ankle angle velocity. Here, we provide the first experimental evidence that lower shortening velocities of the soleus muscle improve running economy.
•Heat exchanger employed influences the system efficiency.•Significant heat loss observed from engine block at part-load.•Variable expander-to-engine speed gear ratio gives a small gain in ...power.•Performance comparison for unique Scandinavian motorway data.
Strict legislations over emissions from heavy-duty trucks are pushing the manufacturers towards improving their brake thermal efficiency, thereby mitigating fuel consumption and reducing CO2 emissions. Organic Rankine cycle-based waste heat recovery system has proven to be an inevitable technology in boosting the engine performance besides the other methods and approaches. In addition to recovering the exhaust heat from the engine, recovering heat from the engine coolant is also beneficial, provided its nominal temperature is raised. Thus, this work investigates the scope of improvement in performance of a heavy-duty truck engine when integrated with a dual-loop organic Rankine cycle system for recovering heat from its exhaust and coolant, simultaneously. The analysis has been performed as a simulation study on GT-SUITE using the one-dimensional model of the engine with its organic Rankine cycle heat recovery setup. The model was developed based on the components of a real commercial truck engine connected with a simple exhaust waste heat recovery system. For the work described in this paper, model of the single-loop exhaust waste heat recovery system was modified to a dual-loop circuit comprising of two scroll expanders and R1233zd(E) as the working fluid. Notably, performance investigation was carried out using a unique Scandinavian motorway road data retrieved from the truck. This paper addresses the challenges associated with simultaneous heat recovery from engine exhaust and coolant. Performance comparison at four steady-state engine operating points reveal that the low temperature radiator installed for the indirect condensation of the working fluid is the major influencing component on system efficiency. At higher engine loads, the overall system efficiency considerably decreased due to limited heat rejection capacity of this radiator. Moreover, on assessing the scope of improving the system’s performance by having variable gear ratio between the engine and the expanders, 1.6 % points (0.12 kW) gain in power was observed by having the high-pressure expander’s speed fixed and the low-pressure expander’s speed varied. Furthermore, elevating the engine coolant temperature from 120 °C to 140 °C, significant heat loss from the coolant to the engine surroundings resulted in a substantial drop in net power at lower part loads although it had improved at higher engine operating points.
Changes in muscle shape could play an important role during contraction allowing to circumvent some limits imposed by the fascicle force–velocity (F–V) and power–velocity (P–V) relationships. Indeed, ...during low-force high-velocity contractions, muscle belly shortening velocity could exceed muscle fascicles shortening velocity, allowing the muscles to operate at higher F–V and P–V potentials (i.e., at a higher fraction of maximal force/power in accordance to the F–V and P–V relationships). By using an ultrafast ultrasound, we investigated the role of muscle shape changes (vastus lateralis) in determining belly gearing (muscle belly velocity/fascicle velocity) and the explosive torque during explosive dynamic contractions (EDC) at angular accelerations ranging from 1000 to 4000°.s
–2
. By means of ultrasound and dynamometric data, the F–V and P–V relationships both for fascicles and for the muscle belly were assessed. During EDC, fascicle velocity, belly velocity, belly gearing, and knee extensors torque data were analysed from 0 to 150 ms after torque onset; the fascicles and belly F–V and P–V potentials were thus calculated for each EDC. Absolute torque decreased as a function of angular acceleration (from 80 to 71 Nm, for EDC at 1000 and 4000°.s
–1
, respectively), whereas fascicle velocity and belly velocity increased with angular acceleration (
P
< 0.001). Belly gearing increased from 1.11 to 1.23 (or EDC at 1000 and 4000°.s
–1
, respectively) and was positively corelated with the changes in muscle thickness and pennation angle (the changes in latter two equally contributing to belly gearing changes). For the same amount of muscle’s mechanical output (force or power), the fascicles operated at higher F–V and P–V potential than the muscle belly (e.g., P–V potential from 0.70 to 0.56 for fascicles and from 0.65 to 0.41 for the muscle belly, respectively). The present results experimentally demonstrate that belly gearing could play an important role during explosive contractions, accommodating the largest part of changes in contraction velocity and allowing the fascicle to operate at higher F–V and P–V potentials.
The number of electric vehicles (EVs) has increased sharply with the start of the 21st century. Although the automobile industry believes that drivetrains equipped with two-speed transmission can ...increase the energy efficiency of EVs by 4–5% and improve other vehicle performance indicators, most EVs still use fixed-speed ratio reducers. Does the two-speed transmission make sense? What is the latest development in the industry? What are the reasons this has not yet been popularized? This article attempts to analyze the current situation in-depth and provide a forecast of technology development trends. First, the authors analyze the advantages of the two-speed transmission from the energy consumption, economy, dynamic performance, and other indicators of EVs. Second, the topology optimization of the non-power-interruption two-speed transmission is introduced, and many efforts have been made to analyze the numerous studies both in academic research and industrial development. Then, a unified index for the necessity of adopting a two-speed transmission in EVs is given, which is verified by numerous data of different passenger cars and commercial vehicles. Finally, the authors predict that two-speed transmissions will be used first in sports cars, luxury cars, and electric logistics vehicles within several years, and then gradually penetrate ordinary family cars.
•Analyze the advantages of the two-speed transmission of electric vehicles.•Introduce the topology optimization of two-speed transmission.•Give a unified index for the necessity of adopting a two-speed transmission.•Make predictions on the development trend of two-speed transmissions.
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