Abstract: The present invention relates to a differential gear equipped with a selectively controllable locking device. Said locking device is self energizing, i.e. it utilizes the differentiation energy (i.e. the possible torque imbalance) to self-lock on its own accord. The control signal is therefore not needed to lock the locking device but rather to selectively control it not to lock itself. Said control signal is designed to, separately for each of the two possible differentiation directions, allow or not allow the locking device to lock. In this way the differential gear will get four different working modes. Said working modes are respectively; open regardless of differentiation direction; open in one differentiation direction but self-locking in the other direction; open in the other direction but self-locking in the first one; self-locking regardless of differentiation direction. A control unit is supplied with sensor data of the present “driving situation”. Said control unit has a steering strategy.