Clutch for a cooling fan of a motor vehicle and method of making the same

Claim 1

In a method of making a clutch for a cooling fan of a motor vehicle, said clutch comprising a shaft having a first end to be attached to a rotable member of the motor vehicle and having a second end defined by a cylindrically shaped knurled portion and an adjacent second portion, said knurled portion having protuberances defined by slots formed in the exterior of said shaft, said knurled portion having an outer diameter and having an inner edge adjacent said second portion and an outer edge adjacent said first end, a bearing means having an inner race member press-fitted onto said knurled portion, a housing comprising a body member and a plate member secured together to form an enclosed chamber for holding a viscous fluid, said housing having means for mounting a fan, said body member having a central opening defined by structural means, said bearing means being disposed in said central opening of said body member and engaging said structural means such that said bearing means supports said body member and hence said housing for rotation, and a drive plate having a central opening defined by inner structure press-fitted onto said second portion of said shaft, the improvement comprising the step of forming said shaft before using said shaft to form said clutch with a solid ring shaped portion between said knurled portion and said second portion and next to said inner edge of said knurled portion and with said solid ring shaped portion having an outer diameter about equal to that of said outer diameter of said knurled portion so as to have part of said inner race member of said bearing means be adapted to be press-fitted thereon whereby said solid ring shaped portion is adapted to block the flow of said viscous fluid out of said enclosed chamber by way of said slots which define said protuberances of said knurled portion, said step of forming said shaft comprising the steps of first forming said knurled portion with said proturberances so that said knurled portion has a diameter larger than said solid ring shaped portion and then burnishing said proturberances and said solid ring shaped portion to about the same diameter, and then press-fitting said bearing means on said knurled portion of said shaft so that said part of said inner race member of said bearing means remains press-fitted on said solid ring shaped portion.