Patent ID: 6039138
Filing Date: 2000-03-21
Classification: B60K

Abstract:
In a four-wheel drive vehicle with free wheels including a transfer case having a switching mechanism for switch-over between two-wheel drive and four-wheel drive, and a free wheel hub mechanism for making each of drive-side wheels free by an intake pipe negative pressure in a two-wheel drive condition of said transfer is disposed between each of said drive-side wheels and a drive-side axle, said free wheel hub mechanism including a plurality of sealing members for maintaining a negative pressure path in a hermetically sealed condition, the improvement comprising a negative pressure introducing passage for introducing the intake pipe negative pressure into said free wheel hub mechanism and a negative pressure change-over valve for opening and closing said negative pressure introducing passage and for causing said negative pressure introducing passage to be open to the atmosphere, and a timer means to operate said negative pressure change-over valve in such a manner that said negative pressure introducing passage is opened to the atmosphere after the lapse of a certain time from when said transfer case switches over to two- or four-wheel drive until when the intake pipe negative pressure becomes constant, and said timer means operates said negative pressure change-over valve in such a manner that said negative pressure introducing passage is opened to the atmosphere when the condition of a certain level or higher intake pipe negative pressure has continued a certain period of time after turning on a vacuum switch provided in said negative pressure introducing passage.