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.

In order to improve the performance of the electromagnet for electro-hydraulic proportional valve used in shock absorber, the static and dynamic characteristics of the proportional electromagnet are simulated and analyzed, which provides theoretical basis for the design and optimization of structural parameters of the proportional electromagnet. In this paper, the magnetic circuit model and finite element simulation model of the proportional electromagnet used in shock absorber are established, and the Ansoft software is applied to analyze the influence of the key structural parameters of the proportional electromagnet on static output force and dynamic characteristics. The results demonstrate that with the increase of the depth of basin mouth, the effective travel of the proportional electromagnet increases, and the mean value of the electromagnetic force in the working range decreases. The larger the radial clearance between armature and guide sleeve is, the smaller the electromagnetic force in the effective travel is. When the depth of the basin mouth is 3.9 mm, the slope of the magnetic isolation ring is 35 • , the chamfer length of the convex platform is 0.2 mm, and the radial clearance is 0.3 mm, the proportional electromagnet has good displacement-force and current-force characteristics. According to the further transient analysis, it is found that when the voltage amplitude is 24 V, the rise time of the electromagnetic force under step excitation signal is about 40 ms.

Purpose The purpose of this paper is to study the influences of the oil film thickness between the friction pairs, the rotational speed of the active and passive friction disks and the inlet pressure of the lubricant on the transmission efficiency. Design/methodology/approach A mathematical model of transmission efficiency was established, and the efficiency of transmission was studied by means of numerical analysis. Findings The results demonstrate that the transmission efficiency decreases with the thickness of the oil film increases. When the thickness of oil film d = 0.1 mm, the relationship between transmission efficiency and transmission ratio is linear, that is, with the transmission ratio increases, the transmission efficiency also increases which does not change with the inlet pressure changes. However, when d = 0.1 mm, their relationship is non-linear; the efficiency increases first and then decreases as the transmission ratio increases, but decreases as the inlet pressure increases. Originality/value The authors obtained a rule is that increasing the rotational speed and reducing the inlet pressure of the lubricating oil can improve the transmission efficiency. This study can provide a theoretical basis for power transmission designing of hydro-viscous clutch.

Purpose The purpose of this paper is to study the temperature characteristics of hydro-viscous clutch with different structure of friction disks and obtain the distribution of film temperature. Design/methodology/approach The mathematical model of oil film between friction disks with radial grooves is established. Based on the flow rate equation, the temperature rise equation of oil film is deduced. Considering two-phase flow, the temperature distribution in the oil shear stage and the effects of the ratio of inner radius to outer radius on film temperature rise is studied by using computational fluid dynamics (CFD) technology. Findings The results show that when input speed is constant, the increase in the ratio of inner to outer radius leads to an increase in the peak temperature and the decrease in the ratio results in a larger increasing rate of temperature. Originality/value These results are of interest for the study of hydro-viscous drive and its applications. This study can also provide a theoretical basis for the mechanism of temperature rise by considering the effect of two-phase flow.

Purpose The purpose of this paper is to use the viscosity of fluid to transmit power known as the hydro-viscous drive (HVD) to research the effect of two-phase flow on transmission characteristics. Design/methodology/approach In this paper, a 3D computational model of oil film between friction pair was built to study the transmission characteristics of a two-phase oil film, and the distribution contours of pressure and temperature of oil film were investigated using the computational fluid dynamics technology. Findings The finding of the paper suggests that the distribution law of pressure and temperature of two-phase oil film is almost linear along the radial direction. However, since the physical phenomena near the outlet of the oil film are entirely different, there exists fluctuation. Meanwhile, the volume fraction of air was obtained at different rotation speeds, and the maximum value is 10.55 percent. Compared to the single-phase oil film, the torque transferred by the oil film is not linear with the rotation speed, its value decreases gradually. Originality/value This paper’s conclusions are very important for the study of HVD and its applications, which provide a new idea to further study the mechanism of oil film transmission and its cavitation. The development of fluid viscous speed clutch is dedicated to a large industrial fan and water pump speed regulation and energy saving. With the successful application of the technology, it will have more wide applications in different fields, such as, in steel, water, petrochemical, power plant of slag pump and exhaust fan.