Method for motion control of an axially displaceable shift sleeve in a stepped gear transmission during a synchronization and gear engagement sequence for avoiding gear teeth interference between sleeve teeth of said shift sleeve and gear teeth of a constant mesh gear wheel, wherein the stepped gear transmission comprises said shift sleeve arranged on and rotationally secured to a shaft, and said gear wheel arranged on and rotatable relative to said shaft, the method comprising: - receiving a gear shift command, characterised in that the method further comprising: - determining a target relative displacement (y*_sg) in a radial direction between sleeve teeth and gear teeth of the aforementioned shift sleeve and gear wheel for a state when a gear wheel rotational speed (ω_g) reaches a shift sleeve rotational speed (ω_s) at an end of a synchronisation phase, which target relative displacement (y*_sg) is determined for avoiding impact between sleeve teeth and gear teeth during a following gear engagement phase, - determining a first phase plane trajectory (y_sg1) defining a relationship between a rotational speed difference (ω_sg) between the shift sleeve and the gear wheel and a relative displacement (y_sg) between the sleeve teeth and the gear teeth, wherein the relative displacement (y_sg) according to the first phase plane trajectory (y_sg1) equals the target relative displacement (y*_sg) when said rotational speed difference (ω_sg) becomes zero at the end of the synchronisation phase, - determining a second phase plane trajectory (y_sg2) defining the relationship between the rotational speed difference (ω_sg) between the shift sleeve and the gear wheel and the relative displacement (y_sg) between the shift teeth and the gear teeth (24, wherein the relative displacement (y_sg) according to the second phase plane trajectory (y_sg2) equals the target relative displacement (y*_sg) when said rotational speed difference (ω_sg) becomes zero at the end of the synchronisation phase, - applying a synchronisation torque (T_synch), - controlling said synchronisation torque (T_synch) for keeping a detected real relative displacement (y_sgr) between the sleeve teeth and the gear teeth within the boundaries of the first and second phase plane trajectories (y_sg1, y_sg2) for any rotational speed difference (ω_sg), such that the real relative displacement (y_sgr) between the sleeve teeth and the gear teeth reaches said target relative displacement (y*_sg) simultaneously with said rotational speed difference (ω_sg) becomes zero at the end of the synchronisation phase. - receiving a gear shift command, - determining a target relative displacement (y*_sg) in a radial direction between sleeve teeth and gear teeth of the aforementioned shift sleeve and gear wheel for a state when a gear wheel rotational speed (ω_g) reaches a shift sleeve rotational speed (ω_s) at an end of a synchronisation phase, which target relative displacement (y*_sg) is determined for avoiding impact between sleeve teeth and gear teeth during a following gear engagement phase, - determining a first phase plane trajectory (y_sg1) defining a relationship between a rotational speed difference (ω_sg) between the shift sleeve and the gear wheel and a relative displacement (y_sg) between the sleeve teeth and the gear teeth, wherein the relative displacement (y_sg) according to the first phase plane trajectory (y_sg1) equals the target relative displacement (y*_sg) when said rotational speed difference (ω_sg) becomes zero at the end of the synchronisation phase, - determining a second phase plane trajectory (y_sg2) defining the relationship between the rotational speed difference (ω_sg) between the shift sleeve and the gear wheel and the relative displacement (y_sg) between the shift teeth and the gear teeth (24, wherein the relative displacement (y_sg) according to the second phase plane trajectory (y_sg2) equals the target relative displacement (y*_sg) when said rotational speed difference (ω_sg) becomes zero at the end of the synchronisation phase, - applying a synchronisation torque (T_synch), - controlling said synchronisation torque (T_synch) for keeping a detected real relative displacement (y_sgr) between the sleeve teeth and the gear teeth within the boundaries of the first and second phase plane trajectories (y_sg1, y_sg2) for any rotational speed difference (ω_sg), such that the real relative displacement (y_sgr) between the sleeve teeth and the gear teeth reaches said target relative displacement (y*_sg) simultaneously with said rotational speed difference (ω_sg) becomes zero at the end of the synchronisation phase.