Motor assembly comprising a brushless dc motor with control electronics

Abstract

A motor assembly (101), comprising a brushless DC motor (102) with control electronics (103) which comprises at least two magnetic field sensors adapted to measure magnetic flux from magnetic poles on a rotor in the brushless DC motor (102). The magnetic field sensors are adapted to determine an angular position of the rotor, with the purpose of controlling the current to the brushless DC motor based on the determined angular position. The brushless DC motor is an external rotor motor (102) comprising an internal stator (104), and an external rotor (105) having a periphery (106) and an inside (107), which exhibits a plurality of permanent magnets (108, 109, 110, 111) disposed at regular intervals along the inside (107) to provide the magnetic poles. The magnetic field sensors (112, 113) are disposed at a distance from each other in the proximity of the periphery (106) to measure the magnetic flux leaking radially through the external rotor (105) from the permanent magnets (108, 109, 110, 111) on the inside (107).

We claim: 
     
         1 . A motor assembly, comprising a brushless DC motor with control electronics, wherein said control electronics comprises at least two magnetic field sensors adapted to measure magnetic flux from magnetic poles on a rotor in said brushless DC motor, and wherein said magnetic field sensors are adapted to determine an angular position of said rotor, based on said measurement of magnetic flux, with the purpose of controlling the current to said brushless DC motor based on said determined angular position,
 wherein the brushless DC motor is an external rotor motor, comprising an internal stator and an external rotor,   that said external rotor has a periphery and an inside, exhibiting a plurality of permanent magnets,   wherein said permanent magnets are disposed at regular intervals along said inside to provide said magnetic poles, and   wherein said at least two magnetic field sensors are disposed at a distance from each other in the proximity of said periphery to measure said magnetic flux leaking radially through said external rotor from said permanent magnets on said inside, and   said control electronics comprises at least one planar circuit board oriented tangentially to the periphery of said external rotor, wherein said at least two magnetic field sensors are mounted on said circuit board.   
     
     
         2 . The motor assembly according to  claim 1 ,
 wherein said external rotor motor has more than 6 magnetic poles on said external rotor.   
     
     
         3 . The motor assembly according to  claim 1 , wherein the distance between two of said magnetic field sensors corresponds to about 90 degrees displacement in the electrical cycle of said brushless DC motor. 
     
     
         4 . The motor assembly according to  claim 1 ,
 wherein said at least two magnetic field sensors are adapted to produce measurement signals from said measurement of the magnetic leakage flux, wherein said control electronics comprises at least one microprocessor adapted to read said measurement signals and estimate the angular position of said external rotor in the electrical cycle of said brushless DC motor based on said measurement signals.   
     
     
         5 . The motor assembly according to  claim 4 ,
 wherein said microprocessor is adapted to estimate said angular position by using inverse trigonometry, preferably implemented by table look-up and interpolation.   
     
     
         6 . The motor assembly according to  claim 4 ,
 wherein said microprocessor is adapted to improve the accuracy of said estimation even further by applying a calibrating curve to the estimated angular position.   
     
     
         7 . (canceled) 
     
     
         8 . The motor assembly according to  claim 1 ,
 wherein said at least two magnetic field sensors, said at least one microprocessor with necessary software, said at least one circuit board, and other components included in said control electronics together form a control system, wherein said control system and said brushless DC motor are integrated into a common housing.   
     
     
         9 . The motor assembly according to  claim 8 ,
 wherein said housing comprises at least one aluminium profile against which said circuit board is mounted, wherein said aluminium profile is designed to be capable of serving as both a cooling flange and a casing of the motor.   
     
     
         10 . The motor assembly according to  claim 8 ,
 wherein said at least two magnetic field sensors, said at least one microprocessor, and said other components included in the control system are disposed on one and the same circuit board.   
     
     
         11 . The motor assembly according to  claim 8   claims 8 - 10 ,
 wherein the control system integrated into the motor assembly constitutes a feedback control system adapted to control position, speed or acceleration of said external rotor.   
     
     
         12 . The motor assembly according to  claim 1 ,
 wherein the motor assembly exhibits at least one communication port for connection to an external unit.   
     
     
         13 . The motor assembly according to  claim 9 ,
 wherein said at least two magnetic field sensors, said at least one microprocessor, and said other components included in the control system are disposed on one and the same circuit board.   
     
     
         14 . The motor assembly according to  claim 2 ,
 wherein the distance between two of said magnetic field sensors corresponds to about 90 degrees displacement in the electrical cycle of said brushless DC motor.   
     
     
         15 . The motor assembly according to  claim 5 ,
 wherein said microprocessor is adapted to improve the accuracy of said estimation even further by applying a calibrating curve to the estimated angular position.