Cooling device, electric motor and machine tool

The invention relates to a cooling device for cooling a rotating shaft (20), comprising a rotating shaft (20), a coolant channel (16) formed at least by a wall (26) of the shaft (20), a coolant inlet(12) connected to a coolant channel (16) in flow technology and a coolant outlet (14) connected to the coolant channel (16) in flow technology and is characterized in that the coolant inlet (12) and the coolant outlet (14) are directly flow-connected to each other through a bypass (18). 本发明涉及一种用于冷却旋转轴(20)的冷却装置，包括旋转轴(20)、至少由轴(20)的壁(26)形成的冷却剂通道(16)、与冷却剂通道(16)在流动技术上连接的冷却剂入口(12)以及与冷却剂通道(16)在流动技术上连接的冷却剂出口(14)，其特征在于，所述冷却剂入口(12)和冷却剂出口(14)通过一个旁路(18)彼此直接流动连接。