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Magnetorheological fluids, especially those in high-power magnetorheological devices, inevitably work at high temperatures because of the wall slip, energized coils and frictions between particles. In order to prepare a magnetorheological fluid for high temperatures, this work investigates the properties of three main components (soft magnetic particles, surfactants and base carrier fluids) for a magnetorheological fluid at high temperatures. On this basis, a novel magnetorheological fluid for high temperatures is prepared. Its sedimentation stability, viscosity and shear yield stress are investigated at high temperatures. The results show that the novel magnetorheological fluid has acceptable sedimentation, suitable viscosity and stable shear yield stress at high temperatures. The novel magnetorheological fluid for high temperatures can be applied to most magnetorheological devices, especially high-power magnetorheological devices.

In order to reveal the influence of rotating speed on the stability of torque transmission by magnetorheological fluid, magnetic force, centrifugal force, gravity, stokes resistance and buoyancy of particles are calculated and analyzed. Besides, the rule of particles distribution is simulated by the Fluent software. On this basis, experiments are carried out based on magnetorheological transmission device. The results indicate that the centrifugal force due to rotating speed has greater effect on particles concentration as there is no magnetic field, and particle concentration mainly appears at the outer diameter of disk, but its effects are concentrated only in a smaller area, which will enhance the local working magnetic field. When the particles are subjected to a strong magnetic field, the magnetic force between the particles is much greater than the centrifugal force; thus, the influence of rotating speed can be ignored. The relationship between transmittable torque and rotating speed is not linear due to the hydraulic torque at the speed of 0–80 r/min.

In order to prepare magnetorheological fluid with excellent sedimentation stability, various surfactants are applied to coat carbonyl iron powder. The prepared magnetorheological fluid shows excell...

We report the preparation of a magnetorheological fluid with a high working temperature by using fluorocarbon surfactant and titanate coupling agent as additives at appropriate contents determined by a series of experiments. The sedimentation ratio, apparent viscosity, and yield stress are measured to evaluate the performance of the prepared magnetorheological fluid. Results indicate that AES dispersants, titanate coupling agents, and fluorocarbon surfactants all have improved dispersion properties, and that the compounding fluorocarbon surfactants and titanate coupling agent can further improve the settlement stability of magnetorheological fluid, with < 7 % one-week settlement rate. Diatomite has a good thixotropic effect, and the antisettling effect enhanced with increased content. The types of carrier fluid have no significant effect on the performance of MR fluids. The prepared MR fluid can also work at 180 °C, which is higher than most commercial fluids, and the shear yield stress can reach 50 kPa.

To solve the problem of insufficient stirring in preparation of magnetorheological fluids, the stirring device is optimized by modeling, simulation and experiments. The ordinary agitator is investigated by multiple reference-frame method and Euler–Mixture model, showing that it is of poor stirring effects. On this basis, several monitoring points and lines are selected to monitor the velocity of the agitator in axial, radial and tangential directions. Meanwhile, the varying concentration of solid with time is also monitored to research the influence of blade number, baffle number and stirring speed on stirring performance. The experiments are carried out to evaluate stirring effects of optimized agitator through the sedimentation rate of magnetorheological fluids. The results show that the design of agitator with two-layer blades, six baffles and stirring speed of 20 r/s can significantly reduce the mixing time, about 83%.

Purpose Friction pairs of the hydro-viscous drive speed regulating start device should be designed based on the rated torque. To obtain design basis of the rated torque of the hydro-viscous drive speed regulating start device, studies on effect of torque ratio (a ratio of the load torque to the rated torque) on speed regulating start were carried out theoretically and experimentally. Design/methodology/approach Under different torque ratio, the modified Reynolds, the thermal energy and the viscosity-temperature equations were solved simultaneously by using finite element method to reveal variation laws of the oil film load capacity and torque transmission during the starting process. Then, speed regulating start experiments were carried out to study the following performance of the output speed. Findings The results show that oil film thickness decreases with the increase of the torque ratio; when oil film thickness is less than 0.05 mm, oil film temperature increases rapidly with the decrease of oil film thickness, which eventually deteriorates performance of the speed regulating start; when the torque ratio decreases to about 0.3, output speed shows a better following performance. Originality/value It indicates that, to acquire a better speed regulating start, the rated torque of the hydro-viscous drive speed regulating start device should not be less than three times of the load torque. Achievements of this work provide theoretical basis for optimal design of the friction pairs of the hydro-viscous drive speed regulating start device.

Aiming to solve the problem of magnetorheological transmission heat dissipation, this study designs the magnetic circuit of a water-cooling magnetorheological transmission device based on fundamental electromagnetics theory. Finite element method is used to simulate the magnetic field of the measurement device. Results show that the working magnetic induction can reach 0.56 T when the current is 2.0 A, which can satisfy design requirements. The intensity of magnetic induction in the work space increases with the increase of excitation current and permeability of magnetically conductive material, whereas intensity decreases with the increase of work space size. The thickness and cross-sectional dimension of the guidepost group at the heat-dissipating unit have no significant effect on the intensity distribution of magnetic induction of the entire device.

On the basis of orthogonal experiment, a novel transmission magnetorheological fluid with synthetic ester chain oil as carrier fluid is prepared. The effect of single additive content on the apparent viscosity and settling stability of magnetorheological fluid is analyzed, and the characteristic evaluations are also carried out. The results indicate that the magnetorheological fluid containing 60 wt% carbonyl iron powder has an apparent viscosity of 2.15 Pa·s and can attain the shear yield stress of 36 kPa when the magnetic field strength is 0.5T. Furthermore, the settlement rate of the MRF is less than 3% after two weeks. In comparison with the silicone oil and mineral oil, the synthetic ester chain oil-based magnetorheological fluid has the lowest thermal expansion rate.

To reveal the contact characteristics of the hydraulic brake friction pair during the initial period of braking process and improve its working stability, by using ABAQUS software, we analyzed numerically the contact characteristics of the friction pair, including temperature, contact stress and heat flux variation laws of the contact surface. Theoretical analysis was verified by experiments. The results show that 1) the variations of the circumferential temperature distribution increase at first and then decrease; 2) the maximum value of the contact stress is near the inner edge of the friction disc, from t = 0.15 s the relatively larger contact stresses begin to intersperse on the entire contact surface; 3) heat flux distributions are similar to the temperature distributions; 4) the nonuniformity of the contact characteristics decreases with the increase of the friction disc thickness. It indicates that a friction disc of thickness 6 mm should be selected preferentially in the design of the hydraulic brake.

Aiming to prepare high performance magnetorheological fluid, firstly, oleic acid and sodium dodecyl benzene sulfonate are chosen as surfactants. And then, the mechanical stirring process including stirring time, stirring temperature and stirring speed are optimized by measuring sedimentation ratio and zero-field viscosity. Finally, the properties of prepared magnetorheological fluid are elaborated. The results indicate that the compounding of oleic acid and sodium dodecyl benzene sulfonate can improve the properties of magnetorheological fluid distinctively, and the optimistic compounding content is 4g:4g or 5g:5g. The surfactants adding orders and the second stirring time have little effect on the properties of magnetorheological fluid, while obviously of the first stirring time, temperature and speed. Moreover, the sedimentation ratio of prepared magnetorheological fluid is less than 5.2% in two weeks, the zero-field viscosity is smaller than 0.6 Pa · s at 20℃, and the maximum yield stress is higher than 50 kPa.

Aiming to improve the shear yield stress of magnetorheological fluid, magnetorheological fluids with different particle characteristics are prepared, and the influence rules of particle mass fraction, particle size, nanoparticles content and application temperature on shear yield stress are investigated. Experimental results indicate that shear yield stress increases approximate linearly with the enhancement of particle mass fraction. Particle size and the nanoparticles within 10% mass fraction can improve the shear yield stress effectively. When the application temperature is higher than 100℃, the shear yield stress decreases rapidly because of thermal expansion and thermal magnetization effect.

We report the preparation of a high-performance magnetorheological (MR) fluid by using silane coupling agent and bentonite as additives at appropriate contents determined by a series of experiments. We also adopted a new preparation process that was optimized through an orthogonal experimental design. The effects of process parameters on the sedimentation stability of the MR fluid were determined. Sedimentation ratio, apparent viscosity, and yield stress were measured to evaluate the performance of the MR fluid prepared by the optimized process. Results indicated that the MR fluid exhibited enhanced sedimentation stability when the silane coupling agent and bentonite mass fractions were 2.88% and 3.60%, respectively. Moreover, the effect of the second stirring process on sedimentation stability was found to be more important than the first. The optimal preparation parameters determined for the high-performance MR fluid are as follows: first and second stirring temperature of 20°C, first stirring time of 5...