Abstract: A grinding method comprises steps of simultaneously grinding plural grinding portions of a workpiece by plural grinding wheels T1, T2 moved individually each other, and terminating said grinding by a predetermined grinding wheel T1 prior to a termination of said grinding by the other grinding wheel T2. Whereby, a content of the grinding by each grinding wheel T1, T2 can be same. A grinding condition in each grinding by each grinding wheel T1, T2 can be changed in accordance with a measuring result of the grinding portion in the grinding.

Abstract: A driving force transmission system comprising: a coupling case and a shaft arranged rotatably relative to each other; a pilot clutch and a main clutch for controlling a torque transmission between the coupling case and the shaft; an electromagnet for controlling the actions of the pilot clutch and the main clutch; and oil retaining the functions of the pilot clutch and the main clutch. This system further comprises a coupling case, a shaft, a rotor, and X-ring and an O-ring isolating a coupling oil chamber, in which the pilot clutch and the main clutch are arranged, liquid-tight from the surrounding space.

Abstract: A driving force transmission system comprising: a coupling case and a shaft arranged rotatably relative to each other; a pilot clutch and a main clutch for controlling a torque transmission between the coupling case and the shaft; an electromagnet for controlling the actions of the pilot clutch and the main clutch; and oil for retaining the functions of the pilot clutch and the main clutch. This system further comprises a coupling case, a shaft, a rotor, an X-ring and an O-ring for isolating a coupling oil chamber, in which the pilot clutch and the main clutch are arranged, liquid-tight from the surrounding space.