BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross sectional view showing the structure of the magnetic force sensing device of the present invention;
FIG. 2 is an exploded perspective view showing a first embodiment of the magnetic force conducting plate and the drive circuit board;
FIG. 3 is an exploded perspective view showing a second embodiment of the magnetic force conducting plate and the drive circuit board;
FIG. 4 is a schematic side plan view showing the magnetic flux from the permanent magnet to the Hall element as well as the magnetic force conducting plate is increased; and
FIG. 5 is a schematic side plan view showing the magnetic flux from the permanent magnet to the Hall element in a conventional brushless motor structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIG. 1, it is noted that the magnetic force sensing device in accordance with the present invention is incorporated with a motor having a casing (10), a stator (20) and a rotor (30) both received inside the casing (10). The stator (20) is mounted inside the casing (10) and having therein a coil. The rotor (30) is rotatably mounted inside the casing (10). The magnetic force sensing device includes a drive circuit board (40), a magnet (50) and a magnetic force conducting plate (60).
The drive circuit board (40) is mounted in the casing (10) and has a Hall element (41) electrically connected to the drive circuit board (40) and corresponding to the stator (20).
The magnet (50) is annular and mounted inside a housing of the rotor (30) and outside the stator (20) to keep a distance to an outer periphery of the stator (20). The magnet (50) corresponds to the Hall element (41).
The magnetic force conducting plate (60) is mounted below the drive circuit board (40) to sandwich the Hall element (41) with the magnet (50). The magnetic force conducting plate (60) has an area larger than that of the Hall element (41). Preferably, the magnetic force conducting plate (60) is made of a magnetic force induction material, e.g. metal.
As shown in FIG. 2, it is noted that the magnetic force conducting plate (60) is annular disk and may also be any geometric configuration, such as the rectangular magnetic force conducting plate (60A) shown in FIG. 3.
With reference to FIG. 4, it is noted that after the magnetic force sensing device is mounted inside a motor and the drive circuit board (40) is provided with electricity, the Hall element (41) is capable of sensing the polarity of the magnet (50) corresponding to the induced magnet inside the stator (20) so as to alternately change the polarity of the induced magnet of the stator (20) to always correspond to the polarity of the magnet (50) so that the rotor (30) is rotated. Due to the addition of the magnetic force conducting plate (60,60A) below the drive circuit board (40), the magnetic flux from the magnet (50) to the magnetic force conducting plate (60,60A) helps enhance the sensibility of the Hall element (41) to the polarity of the magnet (50). As a consequence of the addition of the magnetic force conducting plate (60,60A), the efficiency of the motor is maintained.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Patent Application
20080048532
