| 摘要 |
In the operation of a drive system for a motor vehicle comprising means for permanently driving a first pair of wheels and automatically operable means for selectively driving a second pair of wheels in dependence on the slip of the first pair of wheels, a frequent change between a four-wheel drive mode and a two-wheel drive mode for measuring purposes and for speed compariosn should not be required and this should be achieved with structurally simple means. To that end two sensors are respectively associated with the two permanently driven wheels and are operable to generate speed signals representing the speeds of said two wheels and to deliver said signals to a computer, which derives an actual speed difference signal from said speed signals and in which respective characteristic speed differences, which are specific to the vehicle, are stored for the two-wheel drive mode and for the four-wheel drive mode. Said computer is operable to compare said actual speed difference signal with a current reference speed difference which depends on that of said stored characteristic speed differences which is associated with the current mode and in dependence on the result of said comparison to control a final control element for changing the power train from the two-wheel drive mode to the four-wheel drive mode when the comparison indicates that the actual speed difference exceeds the current reference speed difference and from the four-wheel drive mode to the two-wheel drive mode when the comparison indicates that the actual speed difference is lower than the current reference speed difference.
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