Specific Torque Research Articles

Model-based control of a clutch actuator used in hybrid dual-clutch transmissions

The hybridization of automotive powertrains increases due to legislative regulations in order to reduce emissions. Hybrid Dual-Clutch Transmissions, where an electric machine is included in the transmission, play a key role in this topic because of their significantly lower losses in contrast to other transmission concepts. On the one hand the hybridization results in new functionalities such as boosting, electric drive and many more. But on the other hand it also increases complexity and the necessity of improved control algorithms because of the advanced interaction of the engine, the electric machine, the clutches and the vehicle. For a good drivability a fast and precise control of all actuators is mandatory. The key elements here are the clutches as they connect or decouple the propulsion sources from the wheels. In order to meet these requirements, two model-based control approaches are elaborated in this contribution. Beginning with a detailed nonlinear parametric model, it is reduced with two different approaches and the singular perturbation theory. With the reduced models a position-based and a pressure-based controller are designed, both with a Two-Degree-of-Freedom structure that contains a flatness-based feedforward component, a linear–quadratic regulator with integrator as feedback component, an observer for the stiff system, and a trajectory generation module. Both controllers show a fast control response and only small tracking errors in experiments performed on a transmission test bench, where the filling of the clutch and the tracking of several specific torque profiles, such as a fast engagement process are validated.

Spider-Inspired Electrohydraulic Actuators for Fast, Soft-Actuated Joints.

The impressive locomotion and manipulation capabilities of spiders have led to a host of bioinspired robotic designs aiming to reproduce their functionalities; however, current actuation mechanisms are deficient in either speed, force output, displacement, or efficiency. Here—using inspiration from the hydraulic mechanism used in spider legs—soft‐actuated joints are developed that use electrostatic forces to locally pressurize a hydraulic fluid, and cause flexion of a segmented structure. The result is a lightweight, low‐profile articulating mechanism capable of fast operation, high forces, and large displacement; these devices are termed spider‐inspired electrohydraulic soft‐actuated (SES) joints. SES joints with rotation angles up to 70°, blocked torques up to 70 mN m, and specific torques up to 21 N m kg−1 are demonstrated. SES joints demonstrate high speed operation, with measured roll‐off frequencies up to 24 Hz and specific power as high as 230 W kg−1—similar to human muscle. The versatility of these devices is illustrated by combining SES joints to create a bidirectional joint, an artificial limb with independently addressable joints, and a compliant gripper. The lightweight, low‐profile design, and high performance of these devices, makes them well‐suited toward the development of articulating robotic systems that can rapidly maneuver.

Evolution of magnetic field induced ordering in the layered quantum Heisenberg triangular-lattice antiferromagnet Ba3CoSb2O9

Quantum fluctuations in the effective spin one-half layered structure triangular-lattice quantum Heisenberg antiferromagnet Ba$_3$CoSb$_2$O$_9$ lift the classical degeneracy of the antiferromagnetic ground state in magnetic field, producing a series of novel spin structures for magnetic fields applied within the crystallographic ab plane. Theoretically unresolved, however, are the effects of interlayer antferromagnetic coupling and transverse magnetic fields on the ground states of this system. To address these issues, we have used specific heat, neutron diffraction, thermal conductivity, and magnetic torque measurements to map out the phase diagram as a function of magnetic field intensity and orientation relative to the crystallographic ab plane. For H parallel to the ab plane, we have discovered an additional, previously unreported magnetic-field-induced phase transition at low temperature and an unexpected tetracritical point in the high field phase diagram, which - coupled with the apparent second-order nature of the phase transitions - eliminates several theoretically proposed spin structures for the high field phases. Our calorimetric measurements as a function of magnetic field orientation are in general agreement with theory for field-orientation angles close to plane parallel but diverge at angles near plane perpendicular; a predicted convergence of two phase boundaries at finite angle and a corresponding change in the order of the field induced phase transition is not observed experimentally. Our results emphasize the role of interlayer coupling in selecting and stabilizing field-induced phases, provide new guidance into the nature of the magnetic order in each phase, and reveal the need for new physics to account for the nature of magnetic ordering in this archetypal 2D spin one-half triangular lattice quantum Heisenberg antiferromagnet.

Human-robot cooperative control system based on serial elastic actuator bowden cable drive in ExoArm 7-DOF upper extremity exoskeleton

The exoskeleton of the upper limb is an external parallel kinematic chain to the human arm. The device is designed to apply a specific torque of interaction to the human body resulting from bilateral teleoperation or rehabilitation. Its task is to work comfortably with the human arm. This paper presents the structure of the developed device and the control system of its joints. The construction of the joints’ drive system was performed based on the Bowden cable transmission. Based on the Bowden cable flexibility, it is possible to control the generated drive torque following the serial elastic actuator concept. The article presents joint control methods minimizing the influence of friction in the closed-loop Bowden cable conduit system. We also present the methods of estimating the torque of interaction with the operator based on the ExoArm 7-DOF exoskeleton dynamics model.

Analytical model for meshing stiffness, load sharing, and transmission error for spur gears with profile modification under non-nominal load conditions

The loaded tooth deflections, manufacturing deviations, and assembly errors on spur gears induce a delay on the driven gear respect to the driving gear, which is called loaded transmission error. This delay causes an earlier start of contact outside the pressure line, resulting in a mesh-in impact, which is an important source of noise and vibrations. To avoid or mitigate this mesh-in impact, profile modifications on the driven tooth tip are frequently used. The additional gap due to the profile relief delays the effective start of contact, and a suitable amount of relief sets the mesh-in point back to the theoretical inner point of contact, which prevents the mesh-in impact and ensures a smooth contact. However, as the loaded transmission error depends on the transmitted load, a specific amount of relief will be suitable only for a specific input torque. For higher transmitted load mesh-in impact will occur again, while for lower transmitted load the effective contact ratio will be reduced due to an excessive delay of the start of contact. Therefore, under variable load conditions it is not possible to adjust the start of contact to the theoretical inner point of contact, so mesh-in impact, smooth contact and reduction of contact ratio may alternatively occur. In this paper, a simple analytical model for the meshing stiffness, load sharing ratio and transmission error is presented for spur gears with profile modification under non nominal -or variable- load conditions.

Lifelong Ulk1-Mediated Autophagy Deficiency in Muscle Induces Mitochondrial Dysfunction and Contractile Weakness

The accumulation of damaged mitochondria due to insufficient autophagy has been implicated in the pathophysiology of skeletal muscle aging. Ulk1 is an autophagy-related kinase that initiates autophagosome assembly and may also play a role in autophagosome degradation (i.e., autophagy flux), but the contribution of Ulk1 to healthy muscle aging is unclear. Therefore, the purpose of this study was to investigate the role of Ulk1-mediated autophagy in skeletal muscle aging. At age 22 months (80% survival rate), muscle contractile and metabolic function were assessed using electrophysiology in muscle-specific Ulk1 knockout mice (MKO) and their littermate controls (LM). Specific peak-isometric torque of the ankle dorsiflexors (normalized by tibialis anterior muscle cross-sectional area) and specific force of the fast-twitch extensor digitorum longus muscles was reduced in MKO mice compared to LM mice (p < 0.03). Permeabilized muscle fibers from MKO mice had greater mitochondrial content, yet lower mitochondrial oxygen consumption and greater reactive oxygen species production compared to fibers from LM mice (p ≤ 0.04). Alterations in neuromuscular junction innervation patterns as well as changes to autophagosome assembly and flux were explored as possible contributors to the pathological features in Ulk1 deficiency. Of primary interest, we found that Ulk1 phosphorylation (activation) to total Ulk1 protein content was reduced in older muscles compared to young muscles from both human and mouse, which may contribute to decreased autophagy flux and an accumulation of dysfunctional mitochondria. Results from this study support the role of Ulk1-mediated autophagy in aging skeletal muscle, reflecting Ulk1′s dual role in maintaining mitochondrial integrity through autophagosome assembly and degradation.

Analytical Design and Experimental Testing of a Self-Cooled, Toroidally Wound Ring Motor With Integrated Propeller for Electric Rotorcraft

This article presents a ring motor that is wrapped around the outer diameter of a propeller for electric rotorcraft. The approach is motivated by the greater aerodynamic efficiency afforded by larger diameter propellers with lower rotational speeds, ultimately minimizing battery energy requirements in electric rotorcraft. Lower rotational blade speeds are mismatched with electric machines that derive power density from high-speed operation, thus a machine design with very high torque density is proposed to allow lower speed operation without the aid of gearing. By wrapping the machine around the outer diameter of the blades, the innate lever arm drastically increases the torque density of the machine without the need for liquid cooling. An analytical design approach is used to characterize the machine design space and design outcomes are verified with finite-element analysis. The final prototype design targets the “heavy-lift” drone space and was tested to verify performance. Measurements of back electromotive force and max torque per amp, along with unloaded and loaded (propeller) testing, benchmark the design and highlight the relative impacts among the various loss mechanisms. The measured specific torque density of the air-cooled design is 6.25 N·m/kg - total mass, 11.1 N·m/kg - active mass only. Key areas for improvement, such as bearing drag reduction and winding fault tolerance, are identified.

The Influence of Body Fat Distribution on Postural Balance and Muscle Quality in Women Aged 60 Years and Over.

The aim of this study was to investigate the influence of body fat distribution on postural balance and lower-limb muscle quality in women aged 60 years and over. Two hundred and twenty-two volunteers took part in this cross-sectional analysis. Participants underwent body fat distribution assessment using dual-energy x-ray absorptiometry and were classified as nonobese, gynoid obese, or android obese. Postural balance was assessed during quiet standing, with and without vision restriction, using a force platform. Specific torque was defined as the ratio of knee extensors peak torque (evaluated by an isokinetic dynamometer) to the lean mass of the same limb (evaluated by dual-energy x-ray absorptiometry). Compared with nonobese participants, both obese groups exhibited higher range of postural sway along the anteroposterior and mediolateral axes (P < .05). However, there were no differences between participants with gynoid and android obesity. The android obese group exhibited greater speed of postural sway in the condition without vision restriction than both nonobese (P = .040) and gynoid obese (P = .004) groups. Regarding muscle quality, only participants with gynoid obesity (P = .004) presented lower specific torque than their nonobese peers. These results may be clinically useful when designing falls prevention exercises targeting the obese population.

Optimization of Coaxial Magnetic Gear Design and Magnet Material Grade at Different Temperatures and Gear Ratios

Magnetic gears, like mechanical gears, transform power between different speeds and torques; however, magnetic gears' contactless nature provides inherent potential benefits over mechanical gears. A genetic algorithm was used to optimize magnetic gears at different temperatures across a range of gear ratios. Using different magnet material grades on the different rotors and for the tangentially and radially magnetized magnets can slightly increase the specific torque relative to designs with a single magnet material. The high pole count rotor requires a magnet material with higher coercivity than that of the low pole count rotor magnet material, especially for designs with a large gear ratio. While increasing the temperature produces an exponential decay in the achievable specific torque, with a compounding reduction of about 0.4% for each degree Celsius, the temperature does not significantly affect the optimal geometric parameters and primarily affects the optimal materials. The gear ratio significantly affects the optimal geometric parameters and can impact the optimal magnet materials. Additionally, the genetic algorithm was employed to characterize the impact of stack length using 3D finite element analysis. Designs with shorter stack lengths favored thinner magnets and higher pole counts and may be able to use magnet materials with lower coercivities.

Humidity- and Water-Responsive Torsional and Contractile Lotus Fiber Yarn Artificial Muscles.

Materials that dynamically respond to their environment have diverse applications in artificial muscles, soft robotics, and smart textiles. Inspired by biological systems, humidity- and water-responsive actuators that bend, twist, and contract have been previously demonstrated. However, more powerful artificial muscles with large strokes and high work densities are needed, especially those that can be made cost-effectively from eco-friendly materials. We here derive such muscles from naturally abundant lotus fibers. A coiled lotus fiber yarn muscle provides a large, reversible tensile stroke of 38% and a work capacity during contraction of 450 J/kg, which is 56 times higher than that of natural skeletal muscles and higher than that for any other reported natural fiber muscles. In addition, highly twisted lotus fiber yarn muscles provide a fully reversible torsional stroke of 200°/mm of muscle length and a peak rotation speed of 200 rpm, with a generated specific torque of 488 mN·m/kg for a 2.5 cm long muscle. Potential applications of these lotus fiber yarn muscles are demonstrated for a weight-lifting artificial limb and a smart textile.

Высокоэффективный электропривод с системой технического зрения для тягового применения в тяжелых гусеничных машинах

A new type of electric motor as a traction drive DET400 based on a field regulated reluctance machine (FRRM) provides high energy efficiency and high specific torque. A comparison is made between FRRM and various types of traction electric drives. The issues of designing the FRRM are considered, the geometric parameters of the electric machine are optimized to achieve the maximum specific indicators. To expand the functionality and ensure operational safety, it is proposed to introduce computer vision into the electronic control system. As a result, the FRRM is designed for traction applications based on the real requirements of a Russian-made crawler tractor.

Age-Related Changes in Molecular and Whole Muscle Function: Role of Fat Content?

Decreases in muscle size and function are a general consequence of old age; the precise mechanisms of these changes remain unclear. Recent studies suggest that fat deposition in muscle may also contribute to dysfunction in older adults. Fat content was quantified in the quadriceps, and its effects on function in healthy young (21-45 y) and older (65-75 y) men and women (n=44) of comparable physical activity were compared. A subset of the young matched with the older group for muscle fat content were also examined. Peak fat-free whole muscle cross-sectional area (mCSA; cm2), volume (MV; cm3), fat content (fat fraction, FF; %), specific torque (Nm/mCSA) and peak contraction velocity (Nm∙s-1) were determined using fat-water magnetic resonance imaging and dynamometry (0-300□∙s-1). To examine potential molecular mechanisms of muscle weakness, vastus lateralis biopsies were obtained (n=31) and cross-bridge kinetics of type I and II fibers were determined. FF was higher in older adults than young (8.4±1.2% (SE), 7.6±1.4; p=0.03), while mCSA (48.9±10.4 vs. 64.2±17.3), MV (1536±532 vs. 2112±708), specific torque (2.6±0.4 vs. 3.2±0.4), and peak voluntary contraction velocity (422±20 vs. 441±23) were lower in older than young (p<0.01). Type II fiber myosin attachment rate was slower and attachment time longer in older muscle (p<0.017), providing a potential mechanism for the slowing of peak contraction velocity with age. Notably, differences at the whole muscle and molecular levels remained for the subset of young and older groups matched for FF, suggesting that fat deposition in muscle does not exacerbate age-related changes in function.

Sex-Dependent Effects of Quadriceps Fat Content on Single Muscle Fiber Size in Older Adults

Evidence suggests that ectopic fat deposition interferes with skeletal muscle structure and function, but few studies have examined underlying morphological and contractile properties at the single fiber level. Healthy older (65-75 y) men (n=9) and women (n=9) underwent dynamometry for assessment of knee extensor maximal torque, water-fat magnetic resonance imaging to quantify quadriceps muscle cross-sectional area (CSA) and fat fraction (FF), and vastus lateralis biopsies to determine morphology and function of type I and II muscle fibers. Despite similar body mass indices (24.4±1.3 vs. 24.6±0.5 kg∙m2, p=0.93) and daily moderate-to-vigorous physical activity (46±7 vs. 41±9 min∙d-1, p=0.67), women had greater FF (9.0±0.3 [range: 7.6-10.6] vs. 7.9±0.4 [6.0-9.7] %, p=0.04) than men, indicating increased adipose tissue deposition in skeletal muscle. Women also had smaller quadriceps CSA (39.8±1.8 vs. 57.9±1.3 cm2, p=0.01), specific torque (1.5±0.1 vs. 1.9±0.1 Nm∙cm-2, p=0.01) and type II fiber CSA (3,943±312 [2,350-5,140] vs. 5,352±384 [3,560-6,590] µm2, p=0.01) than men. Type I CSA did not differ by sex (4,918±228 [3,740-5,600] vs. 5,630±440 [3,640-7,670] µm2, p=0.19). In older women, FF was inversely associated with single fiber CSA in type I (r= -0.81, p=0.02) and II (r= -0.76, p=0.03) fibers, and tended to be associated with slower myosin-actin cross-bridge kinetics (longer myosin attachment time) in type I fibers (r=0.65, p=0.08). These relationships were not observed in men. Overall, healthy older women have greater intramuscular fat than men, which may contribute to sex-specific effects on knee extensor specific torque through differences in muscle fiber size and cross-bridge kinetics.

Torque and Velocity Dependence of Muscle Fatigue in Aging

Old age generally leads to smaller, weaker and slower skeletal muscles. To address the independent effects of weakness vs. slowing on fatigue in aging, we used a custom ergometer in a whole-body, 3 tesla magnetic resonance system to quantify knee extensor size, torque, velocity, power and intracellular energetics at baseline and during two 4-min fatiguing contraction protocols; one in which contraction velocity was constrained and torque varied (i.e., torque-dependent contractions; isokinetic, IsoK), and one in which torque was constrained and velocity varied (i.e., velocity-dependent contractions; isotonic, IsoT). On separate days, 10 young (27.5±1.2 yrs, 6 men) and 10 older (71.2±1.6 yrs, 5 men) healthy adults completed the IsoK (120°∙s-1, 0.5 Hz) and IsoT (20% maximal torque, 0.5 Hz) protocols, with continuous measures of intracellular [Pi], pH, and [H2PO4-]. At baseline, contractile volume (803.5±72.3 vs. 1,125.6±109.9cm3), specific IsoK torque (0.035±0.004 vs. 0.058±0.007Nm.cm-3) and IsoT velocity (121.4±11.6 vs. 176.3±8.0deg.s-1) were greater in young than older (p≤0.023). Fatigue (%initial specific torque) was greater in young than older for IsoK (40.1±3.0 vs. 61.2±5.3%, p=0.0028), and accompanied by greater [Pi] and [H2PO4-] and lower pH in the young (p≤0.001). For IsoT, fatigue (%initial velocity) was not different between groups (young: 56.5±5.5 vs. older: 47.2±4.9%, p=0.661), despite lower pH and greater [H2PO4-] in young than old (p≤0.001). Collectively, these results reveal that normalizing dynamometer outputs to assess age-related differences in fatigue obscures baseline differences in muscle weakness. Further, our results suggest the contractile machinery may be less sensitive to changes in pH in older than young.

Simplified Design of Magnetic Gear by Considering the Maximum Transmission Torque Line

Magnetic gears (MGs) technology is studied widely among research institutions, with several improvements being documented. This development attracts a high amount of attention due to the demand in the development of magnetic gears towards higher performance than the conventional mechanical counterpart. In general, the design is complicated and there is a lack in detailed references for designing an MG for specific transmission torque as required by its application. Trial-and-error approaches have been the norm in achieving the desired torque by referring the existing MGs for the desired value of torque. This paper presents a new simplified approach towards designing an MG for the required torque and size by referring through a Maximum Transmission Torque Line (MTTL) reference. Finite element method (FEM) is used in analyzing randomly designed magnetic gears with various parameters towards the desired values of the MTTL. The proposed approach of MTTL is a new approach to estimate the total volume of permanent magnets (PMs) required for the MG to achieve the desired transmission torque. The reference line is used to generate equation relating the specific parameters of MG to develop the simplified design of MG based on the estimated total volume of PMs. This simplified way details to 8.5% of error in targeting the desired transmission torque, a means and way for the first stage of the MG design approach to reduce the conventional approaches.

Combined Optimal Torque Feedforward and Modal Current Feedback Control for Low Inductance PM Motors

Small sized electric motors providing high specific torque and power are required for many mobile applications. Air gap windings technology allows to create innovative lightweight and high-power electric motors that show low phase inductances. Low inductance leads to a small motor time constant, which enables fast current and torque control, but requires a high switching frequency and short sampling time to keep current ripples and losses in an acceptable range. This paper proposes an optimal torque feedforward control method, minimizing either torque ripples or motor losses, combined with a very robust and computation-efficient modal current feedback control. Compared to well-known control methods based on the Clarke-Park Transformations, the proposed strategy reduces torque ripples and motor losses significantly and offers a very fast implementation on standard microcontrollers with high robustness, e.g., against measurement errors of rotor angle. To verify the accuracy of the proposed control method, an experimental setup was used including a wheel hub motor built with a slotless air gap winding of low inductance, a standard microcontroller and GaN (Gallium Nitride) Power Devices allowing for high PWM switching frequencies. The proposed control method was validated first by correlation of simulation and experimental results and second by comparison to conventional field-oriented control.

Design Optimization and Comparison of Direct-Drive Outer-Rotor SRMs Based on Fast Current Profile Estimation and Transient FEA

Outer-rotor switched reluctance machines (SRMs) have drawn much attention as promising candidates for in-wheel direct-drive motors of future electric vehicles. This article presents a systematic performance comparison of three outer-rotor SRM topologies for in-wheel traction applications in terms of the specific torque, electromagnetic efficiency, torque ripple, radial force, and mechanical aspects. A generalized design optimization framework for SRMs is proposed to enable the fast evaluation of large numbers of designs generated from the differential evolution by incorporating an analytical current profile estimation into the transient finite element analysis. The relationship between the saliency ratio and converter volt-ampere rating is also discussed. The calculations are then benchmarked with the experimental results from an existing prototype. The effectiveness of the performance prediction method and the proposed optimization approach is validated.

Comparison Between Coreless and Yokeless Stator Designs in Fully-Superconducting Propulsion Motors

Hybrid electric propulsion could be the solution to the ambitious environmental targets of the aerospace industry. Fully-superconducting machines have the potential to deliver the step-change in specific torque, power, and efficiency capabilities required for large civil transport aircraft applications. However, fully-superconducting machines are still in their infancy. This article investigates the electromagnetic design of two different stator design concepts for an ac fully-superconducting machine for an aerospace distributed fan motor application. A benchmark aerospace specification of 1 MW was chosen and the design of a conventional permanent-magnet machine was used to assess the performance of the two equivalent fully-superconducting ac motor designs. Following the guidelines from an experimental study of the losses in a small ac stator prototype with MgB2 coils, a fully-superconducting air-cored stator design and a new yokeless stator design are proposed. Both ac superconducting machine designs use superconducting bulk magnets mounted on a rotor core and an MgB2 superconducting stator winding. This article discusses the key design issues of the two stator layouts in relation to the current aerospace targets for efficiency and power density.

Torque Ripple and Efficiency Online Optimization of Switched Reluctance Machine Based on Torque per Ampere Characteristics

Relatively high torque ripple limits the further development of the switched reluctance machine, and the application of the ripple suppression method will reduce the efficiency of the system. To simultaneously improve the efficiency and torque ripple of the switched reluctance machine, a new commutation and online optimization strategy is proposed. According to the torque per ampere characteristics of the machine, two rotor position angles are defined, which are the boundaries for the high and low torque per ampere operation modes of the two adjacent phases, respectively, and for different operating modes, specific torque hysteresis control schemes are performed. Furthermore, an objective function is constructed with the efficiency and torque ripple coefficient, and during the operation of the machine, the defined boundary angles are online optimized by the genetic algorithm to maximize the value of the objective function. The effectiveness of the method is verified by detailed simulation and experiment under different operating conditions.

Rotor Position Tracking Control for Low Speed Operation of Direct-Drive PMSM Servo System

In this article, a rotor position tracking control (RPTC) strategy is proposed to effectively reduce the speed fluctuation for a direct-drive permanent magnet synchronous motor servo system operating at a low speed with different torque disturbances. In this article, considering the derivative relationship between the rotor position and speed, a speed command is converted to a real-time rotor position trajectory, and then a position-current two-loop control with the RPTC controller is proposed based on the internal model method to smoothly track the rotor position. In addition, the parameter design of the RPTC controller from the perspectives of robust stability and antidisturbance capability is investigated as well. The comparative simulation and experimental results demonstrate that, at a low speed, the proposed RPTC strategy has a good speed performance for both periodic and nonperiodic torque disturbances. Moreover, it enjoys a simple implementation for not requiring the precise speed feedback and specific torque disturbance information.