Analysis and Revision of Torque Formula for Hydro-viscous Clutch

Hydro-viscous clutch is a speed-regulating device for heavy fans and water pumps. It has important engineering significance in the fields of soft-start for rotating machinery. More and more attention has been paid to its torque and control characteristics. This paper is focused on the torque formula for hydro-viscous clutch (HVC), assuming that multi-friction plates distribute ununiformly with different oil film thickness. A mathematical model of friction plates was constructed, then the distribution formula of the oil film thickness was obtained. A new expression was presented using a modified factor. Parameters such as pressure, viscous torque, and oil film thickness were obtained. The results show that each clearance of friction plates is not the same and the distribution of oil film thickness is influenced by pressing force, groove depth, angular ratio of groove/non-groove, and static friction force. To verify the proposed expression, relevant experiments were carried out on an HVC with multi-friction plates, and the experimental results indicate that the new expression is more accurate compared to the original one.

Determining the Viability of the Use of Magneto-Rheological Fluid in a Low Cost Stroke Rehabilitation Device

<p>There are over 15 million people affected by strokes worldwide with a third left disabled. It is estimated that only 5 to 20 % regain upper limb functionality. However, research has shown that repetitive movement on the affected limb improves motor relearning. With the number of people affected by strokes rising each year the demand has begun straining hospital resources, therefore there is a need for some therapy to be moved away from clinical settings and into a person’s home. Robot assisted therapy is a growing field aiming to meet this demand. However currently there are no low cost devices able to actively exercise and strengthen a person’s hand during the acute (early) stage of stroke rehabilitation. This study is a part of a larger project involving the development of a low cost, assistive stroke rehabilitation device requiring a controllable damper. The aim of the study is to determine whether the use of magnetorheological fluid in a controllable damper is viable for use in the planned rehabilitation device. A rotary damper configuration was chosen as it can be made compact and avoid fluid leakage. To be deemed suitable for the application, the viscous torque of the damper needed to be controllable with varying input current. The required damping torques produced must be repeatable and needs to be generated below 34 C, the specified maximum operating temperature of the system. The performance of three vane designs for the rotary damper were investigated. These three designs were layered discs, a paddle and a helix. A test rig using a pulley configuration was designed and constructed to quantify the performance of the vane designs. The test rig recorded the opposing force and temperature measurements for each damper design. The measurements of interest were the off-state (no input current) torque, the achievable torque range, and also the consistency of the measurements. Experiments were conducted with the damper containing air to determine the pre-existing friction between the vane and housing, and water and motor oil were used as the damper fluid to investigate the performance of the designs with known fluid viscosities. Lastly experiments containing magneto-rheological fluid were conducted to determine the controllability and consistency of the viscous torque of each design. The paddle design was selected based on its range and consistency of produced torque, simplicity of the design and expected economical manufacture. With an input current of 0 to 2 A the damper produced a viscous torque range of 0.0036 Nm to 0.044 Nm, which was the equivalent opposing force of approximately 7.3 N. During testing of the various damper designs, a few imperfections were found. A modified version of the chosen damper was constructed to determine whether those features were manufacturing artifacts. It was found that the force measurements became smoother and previous periodic oscillations in the measurements were eliminated. The viscous torque of the paddle design was found to be controllable within the given operational conditions and therefore the use of magnetorheological fluid is a viable solution for use in a low cost stroke rehabilitation device.</p>

Determining the Viability of the Use of Magneto-Rheological Fluid in a Low Cost Stroke Rehabilitation Device

<p>There are over 15 million people affected by strokes worldwide with a third left disabled. It is estimated that only 5 to 20 % regain upper limb functionality. However, research has shown that repetitive movement on the affected limb improves motor relearning. With the number of people affected by strokes rising each year the demand has begun straining hospital resources, therefore there is a need for some therapy to be moved away from clinical settings and into a person’s home. Robot assisted therapy is a growing field aiming to meet this demand. However currently there are no low cost devices able to actively exercise and strengthen a person’s hand during the acute (early) stage of stroke rehabilitation. This study is a part of a larger project involving the development of a low cost, assistive stroke rehabilitation device requiring a controllable damper. The aim of the study is to determine whether the use of magnetorheological fluid in a controllable damper is viable for use in the planned rehabilitation device. A rotary damper configuration was chosen as it can be made compact and avoid fluid leakage. To be deemed suitable for the application, the viscous torque of the damper needed to be controllable with varying input current. The required damping torques produced must be repeatable and needs to be generated below 34 C, the specified maximum operating temperature of the system. The performance of three vane designs for the rotary damper were investigated. These three designs were layered discs, a paddle and a helix. A test rig using a pulley configuration was designed and constructed to quantify the performance of the vane designs. The test rig recorded the opposing force and temperature measurements for each damper design. The measurements of interest were the off-state (no input current) torque, the achievable torque range, and also the consistency of the measurements. Experiments were conducted with the damper containing air to determine the pre-existing friction between the vane and housing, and water and motor oil were used as the damper fluid to investigate the performance of the designs with known fluid viscosities. Lastly experiments containing magneto-rheological fluid were conducted to determine the controllability and consistency of the viscous torque of each design. The paddle design was selected based on its range and consistency of produced torque, simplicity of the design and expected economical manufacture. With an input current of 0 to 2 A the damper produced a viscous torque range of 0.0036 Nm to 0.044 Nm, which was the equivalent opposing force of approximately 7.3 N. During testing of the various damper designs, a few imperfections were found. A modified version of the chosen damper was constructed to determine whether those features were manufacturing artifacts. It was found that the force measurements became smoother and previous periodic oscillations in the measurements were eliminated. The viscous torque of the paddle design was found to be controllable within the given operational conditions and therefore the use of magnetorheological fluid is a viable solution for use in a low cost stroke rehabilitation device.</p>

A Theoretical Analysis of Magnetic Particle Alignment in External Magnetic Fields Affected by Viscosity and Brownian Motion

The interaction of an external magnetic field with magnetic objects affects their response and is a fundamental property for many biomedical applications, including magnetic resonance and particle imaging, electromagnetic hyperthermia, and magnetic targeting and separation. Magnetic alignment and relaxation are widely studied in the context of these applications. In this study, we theoretically investigate the alignment dynamics of a rotational magnetic particle as an inverse process to Brownian relaxation. The selected external magnetic flux density ranges from 5μT to 5T. We found that the viscous torque for arbitrary rotating particles with a history term due to the inertia and friction of the surrounding ambient water has a significant effect in strong magnetic fields (range 1–5T). In this range, oscillatory behavior due to the inertial torque of the particle also occurs, and the stochastic Brownian torque diminishes. In contrast, for weak fields (range 5–50μT), the history term of the viscous torque and the inertial torque can be neglected, and the stochastic Brownian torque induced by random collisions of the surrounding fluid molecules becomes dominant. These results contribute to a better understanding of the molecular mechanisms of magnetic particle alignment in external magnetic fields and have important implications in a variety of biomedical applications.

An Investigation of Viscous Torque Loss in Ball Bearing Operating in Various Liquids

The limited functionality of seals that are used in hydraulic machines to prevent the liquid from leaking into the bearings may result in decrease in machine efficiency and reliability and may cause an accident of the whole hydraulic machine. However, not every damage of seals must result in a shutdown of the whole machine. In case of partially or fully flooded bearings, the machine can temporarily operate with significantly increased input power and with lower efficiency. Such a limited operation of the machine shortens its lifetime and is accompanied by the presence of torque loss on the shaft. The measurement of torque loss can be helpful during the design process of new machines as well as for an analysis of hydraulic losses and efficiency of prototypes. Moreover, the real-time measurement of torque loss can be used for remote online monitoring of hydraulic machines. The aim of this paper is to present primarily an experimental investigation of the viscous torque loss for ball bearings submerged into liquid. The CFD simulation is also included to distribute the total torque loss between the hub and the bearing. The main goal is to modify the drag coefficient, respectively the friction loss coefficient in SKF’s and Palgrem’s empirical model. The new coefficients may provide a prediction of torque loss in the fully flooded bearings which is not possible with existing models. The torque loss characteristics are determined for specific ball bearings too. In contradiction to partially flooded bearing situation, it is obvious from a experiment, that some coefficients in Palgrem’s model and SKF model are dependent on revolutions when bearings are fully flooded. The experimental investigation of viscous torque loss are carried out for various types of ball bearings, all fully submerged into two various liquids, i.e., oil and water.

Mechanics of biofilms formed of bacteria with fimbriae appendages

Gram-negative bacteria, as well as some Gram-positive bacteria, possess hair-like appendages known as fimbriae, which play an important role in adhesion of the bacteria to surfaces or to other bacteria. Unlike the sex pili or flagellum, the fimbriae are quite numerous, with of order 1000 fimbriae appendages per bacterial cell. In this paper, a recently developed hybrid model for bacterial biofilms is used to examine the role of fimbriae tension force on the mechanics of bacterial biofilms. Each bacterial cell is represented in this model by a spherocylindrical particle, which interact with each other through collision, adhesion, lubrication force, and fimbrial force. The bacterial cells absorb water and nutrients and produce extracellular polymeric substance (EPS). The flow of water and EPS, and nutrient diffusion within these substances, is computed using a continuum model that accounts for important effects such as osmotic pressure gradient, drag force on the bacterial cells, and viscous shear. The fimbrial force is modeled using an outer spherocylinder capsule around each cell, which can transmit tensile forces to neighboring cells with which the fimbriae capsule collides. We find that the biofilm structure during the growth process is dominated by a balance between outward drag force on the cells due to the EPS flow away from the bacterial colony and the inward tensile fimbrial force acting on chains of cells connected by adhesive fimbriae appendages. The fimbrial force also introduces a large rotational motion of the cells and disrupts cell alignment caused by viscous torque imposed by the EPS flow. The current paper characterizes the competing effects of EPS drag and fimbrial force using a series of computations with different values of the ratio of EPS to bacterial cell production rate and different numbers of fimbriae per cell.

Effects of groove orientation on transmission characteristics of hydro-viscous film in the parallel-disk system

The disk groove can greatly influence the hydrodynamic behaviors of the rotating film, especially on the cooling performance and the transmission efficiency. In the present work, the effects of groove orientation on the hydro-viscous transmission of the parallel-disk system are investigated. The Reynolds equation and thermal equation, considering tangential Coriolis effect and temperature–viscosity dependency, are derived and solved. The effects of the groove orientation on the shear stress, load-carrying capacity, viscous torque, and transmission efficiency are analyzed. The results reveal that the Coriolis resisting torque can be restrained but the load-carrying capacity declines if the groove orientation is consistent with the rotating direction, and the variation of the transmission efficiency can even be inverted at the turning point of the groove orientation. Therefore, the effects of groove orientation must be paid more attention in the hydro-viscous transmission.

Simulation and experiment of viscous torque for disengaged wet clutches of tracked vehicle

In order to predict the viscous drag loss for tracked vehicles, the drag torque of the friction pair with different grooves was investigated in this paper. The traditional computation method is difficult to adapt for the new kinds of friction plates with complex grooves. A numerical method with the help of CFD models is adopted to simulate the fluid flow status in the grooves and the drag torque was obtained by the accumulation of the discrete viscous force. The simulation results implied that the plates with different kinds grooves were provided with various characteristics of viscous torque and these characteristics could be affected by the rotation direction for the plate with spiral grooves, which are proved in experiment. Meanwhile, it was also found that the two kinds of plates with double arc or spiral grooves, which have different sensitive parameters in drag dissipation, have to perform accurate flow control and clearance design respectively. The simulations and experiments showed that the ‘positive spiral grooves’ friction plates had minimum drag torque in regular heavy-duty conditions. It can be used in transmission system with requirements of limited space and high mobility, which can lead to better heat dissipation and less power loss.

Dynamic transmission of oil film in soft-start process of HVD considering surface roughness

Purpose The purpose of this paper is to study the dynamic transmission of the oil film in soft start process of hydro-viscous drive (HVD) between the friction pairs with consideration of surface roughness, and obtain the distribution law of temperature, velocity, pressure, shear stress and viscous torque of the oil film. Design/methodology/approach The revised soft-start models of HVD were derived and calculated, including average Reynolds equation, asperity contact model, load force model and total torque model. Meanwhile, a 2D model of the oil film between friction pair was built and solved numerically using computational fluid dynamics (CFD) technique in FLUENT. Findings The results show that the maximum temperature gradually reduces from the intermediate range (z = 0.5 h) to the inner side of the friction pair along the direction of oil film thickness. As the soft-start process continues, pressure gradient along the direction of the oil film thickness gradually changes to zero. In addition, tangential velocity increases and yet radial velocity decreases with the increase of the radius. Originality/value In this paper, it was found that the viscous torque calculated by the numerical method is smaller than that by the CFD model, but their overall trend is almost the same. This also demonstrates the effectiveness of the numerical simulation.