Low-u road evaluation device and power distribution control device for four-wheel drive vehicles

A power distribution control device 42 calculates a low-µ information magnitude, associated with the friction coefficient of the road surface, based on the slip rate and the vehicle acceleration operation magnitude. If the low-µ information magnitude exceeds an addition evaluation threshold, the power distribution control device 42 adds the low-µ information magnitude. If the low-µ information magnitude does not exceed the addition evaluation threshold, the power distribution control device 42 subtracts a constant K from a counter. The power distribution control device 42 makes evaluates a road to have a low-µ when the counter exceeds a low-µ evaluation threshold.