Claims:1. A cylindrical rotor means for a brushless DC motor, comprising :

a. a cylindrical (rotor) with plurality of laminates having a central portion including a plurality of first structural laminations, and the said core having two end portions each havinga second structural lamination, such that the first structural lamination has a square plate type profile with a square or rectangle tooth type projection at the four corners of the plate, thereby forming four recesses along four sides of the plate, and the second structural lamination also has a square plate type profile with a square or rectangle tooth type projection at the four corners of the plate, which tooth projection is extended further onto a dove tail projection, thereby forming recesses along four sides of the plate, all of said recesses aligning and defining four cavities longitudinally parallel to the axis of the rotor and also defining longitudinally extending four corners around the core, and

b. a hemispherically curved magnets disposed in the said cavities extending longitudinally on the surface of the said core, the said arrangement characterized in that the said projections of the structural laminates limiting the radial and longitudinal displacement of the said surface mounted magnets.
, Description:FIELD OF INVENTION :

This invention relates generally to a rotor means for a brushless DC motor, and more particularly to a magnet for preventing the break-away from the lamination stack.

BACKGROUND OF the INVENTION :

A brushless DC motor generally an ideal choice for applications that demand efficiency and reliability as BLDC motors do not have brushes and deliver high power-to-volume ratio. A BLDC motor is typically a high performance motor that is capable of providing large amounts of torque over a vast speed range.

Any typical BLDC motor has two main components; the rotor the rotating part and the stator the stationery part. Also other parts of the motor are the stator windings and rotor magnets.

As mentioned above, BLDC motor would include a description of the stationery part of the motor as consisting of a stack or lamination pack containing coils arranged in a specific pattern. The rotating portion of the BLDC would consist of few permanent magnets mounted/embedded in iron lamination on the shaft or mounted to the outside diameter of the laminated rotor. When the stator windings is connected to power source the electromagnetic flux generated in stator iron cross links the permanent magnet flux from the rotor and the resulting torque causes shaft rotation.

There are two typical BLDC motor designs, inner rotor and outer rotor designs. In outer rotor design, the windings are located in the core of the motor. The rotor magnets surround the stator windings.

In inner rotor design, the stator windings surround the rotor and are affixed to the motor’s housing.

As described above, the rotor of a BLDC motor is typically a permanent magnet. By applying DC power to the coil, the coil will energise and become an electromagnet. The stator has a coil arrangement. The operation of a BLDC is based on the simple force interaction between the permanent magnet and electromagnet. The invention is related to this type of BLDC.

OBJECTS OF THE INVENTION :

In prior art suffered to securely retain the surface mounted permanent magnets of the rotor in their proper position without “flying off” the core. Such a problem inherently reduces the efficiency of the motor. The invention is directed towards solving this problem and provide a workable and economical solution to them. It is therefore a general object of the present invention to provide an improved BLDC motor.

It is also an object of the present invention to provide a BLDC motor which securely retains the magnets in their proper position without “flying off” the core. It is yet another object of the present invention to provide a BLDC motor which is economical and efficient in use.

It is still another object to have a BLDC motor with a novel rotor design having surface mounted permanent magnet.

The above and other objects, advantages and features of this invention will become apparent from the detailed description.

DESCRIPTION OF THE DRAWINGS :

The detailed description has been disclosed and by way of example but not intended to limit the present invention, the illustration are given for the sole purpose for the reader to understand the invention easily.

Fig. 1 – is a cross-sectional view of BLDC motor in accordance with an illustrative embodiment of the present invention. This assembly of magnet with lamination is easy and also arrests the radial movement of the magnet.

Fig. 2 – illustrates the shape of the magnet such that it cannot slip out of the lamination stack easily.

Fig. 3A – illustration the lamination stack without dovetail

Fig. 3B – illustration the lamination stack with dovetail

Fig. 4 – illustration the lamination stack with magnet. The end lamination is provided along the slinger in order to arrest the axial movement of the magnet.

Fig. 5 – illustration the lamination stack without magnet

DESCRIPTION OF THE INVENTION :

As stated above, the motor of a typical BLDC motor is made out of permanent magnets. Depending upon the application requirements, the number of poles in the rotor can be varied. By increasing the number of poles, one can improve torque but at the cost of reducing the max possible speed. Another rotor parameter that impacts the max torque is the material used for the construction of the permanent magnet, the higher the flux density of the material, the higher the torque.

With reference to construction of BLDC motor, just like any other electric motor, a BLDC motor has a stator and a rotor. Permanent magnets are mounted on the motor of a BLDC and the stator is wound with a specific number of poles.

The rotor is made of permanent magnet and can be made to vary from 2 to 8 pole pairs with alternate North and South poles.

The rotor consists of a shaft and a hub with permanent magnets arranged to form between 2-8 pole pairs that alternate between North and South poles.

The configurations of surface-mounted permanent magnet BLDC motor is disclosed. The surface-mounted permanent magnet BLDC motor is essentially configured as alternate magnet poles rotating past stationary conductors that carry the current.

Typically both the rotor and stator are typically comprised of a lamination of magnetic steel slices to reduce the eddy current loss.

The rotor is constructed with a cylindrical (rotor) with plurality of laminates having a central portion including a plurality of first structural laminations. The core having two end portions, each having a second structural lamination. The first structural lamination has a square plate type profile with a square or rectangle tooth type projection at the four corners of the plate, thereby forming four recesses along four sides of the plate. The second structural lamination also has a square plate type profile with a square or rectangle tooth type projection at the four corners of the plate, which tooth projection is extended further onto a dove tail projection, thereby forming recesses along four sides of the plate, all of said recesses aligning and defining four cavities longitudinally parallel to the axis of the rotor and also defining longitudinally extending four corners around the core, and a hemispherically curved magnets disposed in the said cavities extending longitudinally on the surface of the said core, the said arrangement characterized in that the said projections of the structural laminates limiting the radial and longitudinal displacement of the said surface mounted magnets.

The inventive step lies in optimizing magnet shape and rotor geometry.

In an illustrative embodiment of the invention, there is provided a BLDC motor having a rotor assembly mounted on a rotor shaft. The rotor assembly has a permanent magnet rotor and a plurality of sequentially stacked rotor laminations positioned between the rotor magnet and the rotor shaft. Each of the rotor laminations is made of laminated iron and has a central aperture therein for receiving and retaining the rotor shaft and including the novel magnet shape and rotor geometry.

As a results of the design of the present invention, the magnets mounted therein do not suffer radial movement and do not fall off the lamination stack.

Beyond the illustration and description, the design can be adapted for instance the motor can be made as 4-pole, 6-pole, 8-pole, 10-pole, 12-pole, etc motor. By merely ensuring that the lamination corners have tooth/dove tail, the objects of the invention can be achieved in any number of embodiments. Since the rotor construction and location of permanent magent have a considerable effect on the motor properties, the invention discloses a construction of rotor assembly which simplifies the assembly and supports retaining the magnets against centrifugal force.

It also permits the use of known arc shaped magnets for construction. As illustrated in the accompanying drawings in one aspect, the rotor assembly is constructed by placing 4 arc-shaped permanent magnets with opposite poles mounted on the outer surface of the rotor to provide flux return paths. The permanent magnets are usually magnetized in the radial or parallel direction. From the structural point of view, such a motor configuration as disclosed provide a natural shield to protect the rotor from its surroundings.

According to the configurations disclosed, the permanent magnets are affixed to the outer surface of the rotor, in a novel construction, which prevents the mounted magnets from flying apart, in high speed applications. The main features of the design disclosed are simple and easy to manufacture and assemble, thereby resulting in low production cost.

The description and illustration have illustrated and described the novel magnetic morphology of the motor with magnets mounted on the surface of the rotor which is operable with any conventional stator winding. The invention is not disclosing some of the mechanical aspects, such as the means of fastening the permanent magnets of the rotor. Any known methods such glue bonding, rotor banding or retaining ring structure may be adapted. This sort of arrangement as disclosed is simple in construction but novel.

In accordance with one of the objects of the invention, the design of the extended corner shaped laminations and with configured magnets provides for the secure retention of the motor magnets in their proper position without “flying off” the core.

While the invention has been particularly illustrated and described with reference to a preferred embodiment, it is to be appreciated by skilled person in the art to create various changes and modifications may be made without deporting from the spirit and scope of the invention.