Cooling system for a motor spindle for a machine tool

A motor spindle unit with an integrated cooling system for use in a machine tool, the unit comprising:

• a spindle housing;
• a workpiece spindle mounted in said housing for rotation about a spindle axis;
• an electric three-phase motor accommodated by the housing and having a rotor and a stator, the rotor surrounding the spindle axis concentric therewith and being rotation-wise fixedly connected to the workpiece spindle, and the stator surrounding the rotor concentric therewith;
• the cooling system having a coolant inlet and a coolant outlet in flow communication with one another by at least one flow path for a coolant to be conducted in a predetermined flow direction along the flow path;
• the flow path comprising a group of coolant channels with, in section through the motor perpendicularly to the spindle axis, (1) at least one inner coolant channel circumscribing the stator at least partially, and (2) at least one outer coolant channel circumscribing the stator at least partially and, with respect to the spindle axis, being located radially outside the inner coolant channel;
• the group of coolant channels enclosing the stator at least to a major extent, and wherein a first end of the outer coolant channel is in flow communication with the coolant inlet, a second end of the outer coolant channel is in flow communication with a first end of the inner coolant channel, and a second end of the inner coolant channel is in flow communication with the coolant outlet so that within the outer and inner coolant channels the predetermined flow direction is oriented at least approximately in a circumferential direction with respect to the spindle axis.