Abstract: The present invention relates to a cooling jacket for cooling a permanent magnet synchronous electric motor, wherein the cooling jacket comprises bearing housing cooling portion and a stator cooling portion, wherein the stator cooling portion comprises stator coolant guiding channel having an enlarged middle section. The flow splitter having a shape that corresponds to the enlarged middle section is disposed at the middle of this enlarged section. The flow splitter has the same height as that of the partition wall, and the upper surface of the flow splitter is curved to form a seal with the inner surface of the stator outer housing. At the middle of the stator coolant guiding channel, there is provided a middle rib that extends in the spiral shape around the circumference of the stator cooling portion. The middle rib has a lower height than the height of the partition wall.