This paper describes the development of the new third-generation electronically controlled all-wheel drive (AWD) coupling that achieves drastically improved drag torque performance and torque accuracy at low temperatures, and contributes to higher fuel efficiency through weight reduction in the driveline. One issue for electronically controlled AWD couplings is an increase in torque due to higher lubricant viscosity at low temperatures, especially below 0℃, because of clutch slide with the lubricant sealed inside the couplings. The developed third-generation electronically controlled AWD coupling addresses this issue by focusing on the surface texture of the electromagnetic clutch. The third-generation coupling also restricts the torque increase by actively utilizing the dynamic pressure between the clutch plates and increasing the clearance of the clutch plates at low temperatures where viscosity increases. This enables further weight reduction in the driveline. In order to reduce drag torque at low temperatures, a macroscopic sliding surface profile in the order of tens of micrometers is provided on the electromagnetic clutch under fluid lubrication. In addition, to reduce control torque at low temperatures when current is applied, the microscopic sliding surface profile on the electromagnetic clutch, which is in the order of several micrometers, is optimized under boundary lubrication. This results in stable torque accuracy at both low and high temperatures.
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