In order to prepare magnetorheological fluid with excellent sedimentation stability, various surfactants are applied to coat carbonyl iron powder. The prepared magnetorheological fluid shows excellent sedimentation stability when the surfactants are respectively sodium lauryl alcohol phosphate, compound sodium fatty acid methyl ester sulfonate, ethylene glycol monostearate and glyceride monostearate. Orthogonal tests are carried out for the optimal combination of surfactants and thixotropic agent. The experimental results show that the optimal combination of additives for MRF is 1.5 wt% of sodium lauryl alcohol phosphate, 1.0 wt% of compound MES, 1.5 wt% of ethylene glycol monostearate, 1.5 wt% of glycerol monostearate and 1.0 wt% of hydrophobic fumed silica. Magnetorheological fluid is prepared by the compound scheme, of which the viscosity is 1.09 Pa·s at 25.9°C and the sedimentation rate is 1.61% after one-week placement. The novel MRF is in excellent sedimentation stability and fluidity.

Magnetorheological (MR) clutches have significant potential in electromechanical interface and are a promising technology with high commercial value in the automotive industry. A quick and precise magnetic circuit modeling method is demanded to calculate performance or optimize design of the MR clutch. Conventional magnetic circuit models present poor accuracy because they often fail to accurately include nonlinearities such as magnetic saturation, magnetic fringing, and magnetic leakage. In this regard, an enhanced magnetic equivalent circuit (EMEC) model based on lumped parameter method is proposed. This model can not only cope with clutch geometry and material properties (nonlinear permeability) but can also consider flux fringing and leakage effects. Combined with the specific structure, formulae for the calculation of fringing permeances and leakage permeances in the magnetic circuit of the MR clutch are presented. Finite-element analysis (FEA) and experimental results show that the proposed EMEC model can provide better accuracy compared with magnetic equivalent circuit (MEC) model from available literature and provide less computational effort compared with FEA. Moreover, the influence of design parameters corresponding to device geometry and material properties on the output flux density is discussed based on the proposed EMEC model. All taken together, the proposed EMEC model provides a comprehensive knowledge in optimize design and performance prediction of MR device.

Magnetorheological fluid (MRF) based clutches have been shown potential importance in terms of torque coupling and control applications. As a key performance indexes of magnetorheological (MR) clutch, response time of magnetic circuit was only qualitatively discussed from finite element analysis and experimental testing in previous studies. Response delay in magnetic circuit of MR clutch contributes primarily to eddy current effects in the solid magnetic core and MRF. A simple yet accurate analytical model containing eddy-current effect would be highly beneficial during the design stage to determine the impact of device geometric and material properties on dynamic performance of MR devices. Aim at this issue, based on the combination of the magnetic equivalent circuit approach and eddy current effects, a dynamic analytical model for response time of MR clutch is proposed for the first time. The proposed model is capable of accounting for device material and geometric properties and providing fast, yet accurate solutions. The experimental test and finite element analysis from frequency response are used to verify the feasibility of the proposed model. Moreover, the model has been implemented to investigate the influence of the design parameters on the response time of MR device. All taken together, the analytical model provides a comprehensive knowledge in optimizing design and performance prediction of MR devices.

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. The novel magnetorheological fluid for high temperatures can be applied to most magnetorheological devices, especially high-power magnetorheological devices.