Brushless DC motor

A brushless DC motor, comprising:

• a rotor assembly including a rotatable shaft and a permanent magnet affixed to the shaft, said permanent magnet for generating a magnetic field;
• a winding form enclosing the rotor assembly;
• a plurality of coils wound upon the winding form for producing a magnetic field for applying a torque to the rotor assembly, said coils including end turns that enclose the rotor assembly such that the rotor assembly is not removable, wherein said coils are connected in a three phase delta configuration having a positional relationship with the permanent magnet;
• a stator stack made of a stator magnetic material for providing a magnetic flux return path for the magnetic field of the permanent magnet;
• a position sensor system for sensing the positional relationship that the coils have with the permanent magnet;
• and
• a controller coupled to the position sensor for controlling the application of a power source to the coils in response to the positional relationship of the coils and the permanent magnet.

A cordless power tool, comprising;

• a power module for supplying electrical energy to the brushless DC motor;
• a brushless DC motor for converting electrical energy to mechanical energy, including;
• a rotor assembly having a rotatable shaft and a permanent magnet affixed to the shaft, said permanent magnet for generating a magnetic field;
• a winding form enclosing the rotor assembly;
• a plurality of coils wound upon the winding form for producing a magnetic field for applying a torque to the rotor assembly, said coils including end turns that enclose the rotor assembly such that the rotor assembly is not removable, wherein said coils are connected in a three phase delta configuration;
• a stator stack made of a stator magnetic material for providing a magnetic flux return path for the permanent magnet magnetic field;
• a position sensor system for sensing the positional relationship between the permanent magnet and the plurality of coils;
• and
• a controller, responsive to said position sensor, for controlling the supply of power to the brushless DC motor;
• and
• a tool interface for interfacing the DC motor with a tool;
• and
• a housing for enclosing the power module, controller and DC motor.

A method of constructing a brushless DC motor, comprising the steps of:

• providing magnetizable material to be used in the formation of a permanent magnet;
• bonding the magnetizable material to a rotatable shaft, whereby a rotor is assembled;
• winding a plurality of coils about the rotor such that an air gap is maintained between the coils and the rotor;
• and
• providing a magnetic flux return path for magnetic flux that flows from the rotor.

A DC power tool comprising:

• a housing defining an interface for mechanically and electrically mating with a power module;
• a brushless DC motor operable in a preselected voltage range to convert electrical power to mechanical power, the brushless DC motor comprising;
• a rotor assembly including a rotatable shaft and a permanent magnet affixed to the shaft;
• a slotless wound stator including a winding form that encircles the rotor assembly such that an air gap is maintained between the winding form and the rotor assembly, and a plurality of coils for producing a magnetic field for applying a torque to the rotor assembly, said coils being wound about an outer surface of the winding form;
• and
• a stator stack made of a stator magnetic material for providing a magnetic flux return path;
• and
• a power supply module mechanically and electrically configured to connect to a source of electric power and to mate with the low-voltage DC power tool, said power supply module being adapted to provide a DC voltage in the preselected voltage range suitable for powering the low-voltage DC power tool.

A brushless DC motor, comprising;

• a rotor assembly including a rotatable shaft having a permanent magnet affixed to the shaft;
• an encapsulated stator defining an interface with the rotor assembly such that an air gap is formed;
• the stator comprising;
• a plurality of coils for producing a magnetic field to apply a torque to the rotor assembly;
• and
• a stator stack made of a stator magnetic material for providing a magnetic flux return path;
• and
• a seal applied to the interface being adapted to seal the air gap such that the air gap is blocked off.

A method of constructing a brushless DC motor, comprising the steps of:

• bonding a permanent magnet to a rotatable shaft, whereby a rotor is assembled;
• winding a plurality of coils about the rotor such that an interface is defined having an air gap formed between the coils and the rotor;
• retaining the rotor substantially concentric to the plurality of coils such that the air gap is maintained;
• applying a seal to the interface such that the air gap is sealed;
• and
• applying an impregnation resin to the coils, wherein an encapsulated stator is formed.