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Control Technology of Direct Electromagnetic Clutch Employed in SH-AWD System

Article of Honda R&D Technical Review Vol.17 No.2


The SH-AWD system is a 4WD system providing continuously variable control of the torque transmitted to all four wheels to radically enhance vehicle dynamic performance. The core of the system is a direct electromagnetic clutch positioned in the rear drive unit. This new clutch was developed to enable more precise control than is possible in a conventional electromagnetic clutch. In the direct electromagnetic clutch, there is an air gap between the magnetic materials, that form the solenoid magnetic circuit. The solenoid force generated across this gap is converted into clutch thrust, without the need for the torque amplifier employed in conventional electromagnetic clutches. The fact that thrust acts directly on the clutch increases the precision of control. However, the size of the air gap changes when the thickness of the clutch changes, and this causes change in the solenoid force. A search coil is therefore used to detect changes in the size of the gap as changes in magnetic flux, enabling the current to be corrected in order to ensure that the appropriate solenoid force is consistently generated. In addition, measures to increase the accuracy of detection have enabled more precise control of torque transmission.


(1) Kunii, R., Iwazaki, A., Atsumi, Y., Mori, A.: Development of SH-AWD (Super Handling-All Wheel Drive) System, Honda R&D Technical Review, Vol. 16, No. 2, p. 9-16
(2) Suzuki, K., Ohba, M., Yamamoto, T., Takuno, H.: Development of New Electronic Controlled 4WD system for passenger cars, 1998 JSAE Annual Congress Proceedings, No. 75-98, p. 1-4
(3) Takuno, H., Sakai, T., Sakai, N., Ikeda, A.: Development of New Electromagnetic Controlled Coupling for Four-wheel Drive Vehicles, 1998 JSAE Annual Congress Proceedings, No. 75-98, p. 5-8
(4) Chiba, M., Anan, G.: Hisakusei ni Sugureta Jyuntetsukei Nanjiseizairyou, Kobe Steel R&D Technical Review, Vol. 54, No. 1, p. 117 (2004) (in Japanese)
(5) Iwazaki, A., Kunii, R.: Element Technologies of a Direct Electromagnetic Clutch, 2005 JSAE Annual Congress Proceedings, No. 07-05, p. 23-28

Author (organization or company)

Rikiya KUNII(Tochigi R&D Center)、Yutaka KANNO(Tochigi R&D Center)、Akihiro IWAZAKI(Tochigi R&D Center)、Shigenobu SEKIYA(Tochigi R&D Center)

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