FIELD OF THE INVENTION

[001] The present invention generally relates to a rotary electrical machine, and more particularly to a rotor for the rotary electrical machine. BACKGROUND OF THE INVENTION

[002] A typical rotary electrical machine consists of a stator and a rotor. While the rotor has a set of permanent magnets, the stator contains stacks with slots and winding. The stacks in stator are usually made up of ferromagnetic material. Due to rotation of the rotor, there is change in strength of magnetic field in the stator. [003] It is known that in conventional rotary electric machines, the rotor holds the set of magnets radially inwards. The magnets of the rotor are magnetised in a way that the polarity of the magnets changes alternatively. This alternate arrangement of polarity causes the change in strength of magnetic field in the stator. This change in magnetic field causes a generation of a pulsating torque, also knows as torque ripple. This torque ripple leads to generation of noise. The amplitude of such noise is proportional to the rate of change in strength of magnetic field.

[004] Therefore, it seems apparent that noise can be reduced by reducing the strength of magnetic field. However, a reduction in the strength of magnetic field would also mean that the voltage generation capacity of the electric machine is reduced. Attempts have been made to design rotary electric machine with reduced noise without affecting the voltage generation capacity of the rotary electric machine by placing multiple permanent magnets in a specific orientation and angle with respect to each other. However, this design requires a larger number of permanent magnets than a conventional rotary electric machine, thereby making this design costly and difficult to manufacture. [005] Thus, there is a need in the art for a rotor for a rotary electrical machine which addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION

[006] The present invention is directed towards a rotor for a rotary electric machine having a plurality of magnets. Each magnet has a first region with a first polarity, a second region with the first polarity such that the first region and the second region are adjacent to each other, a third region with a second polarity such that the third region and the second region are connected by a fifth region with the second polarity. Further, the each magnet has a fourth region with the second polarity such that the fourth region is adjacent to the third region and the fourth region is connected to the first region by a sixth region with the first polarity. Herein area of the second region is lower than area of the first region and area of the fourth region is lower than area of the third region, thereby providing a skewed magnetic field strength.

[007] In an embodiment of the invention, the magnets have an arcuate cross section such that the inner curved surface area of each magnet is substantially rectangular when viewed from a centre of the rotor.

[008] In a further embodiment of the invention, the first region and the third region have a rectangular shape, the second region and the fourth region have a trapezoidal shape, and the fifth region and the sixth region have a right-angled triangular shape, when viewed from the centre of the rotor.

[009] In a further embodiment of the invention, a base edge of the fifth region is adjacent to the third region and a hypotenuse edge of the fifth region is adjacent to the second region, and a base edge of the sixth region is adjacent to the first region and a hypotenuse edge of the sixth region is adjacent to the fourth region.

[010] In another embodiment of the invention, area of the first region is equal to area of the third region, area of the second region is equal to area of the fourth region, and area of the fifth region is equal to area of the sixth region. [011] In another embodiment of the invention, the hypotenuse edge of the fifth region and the hypotenuse edge of the sixth region join in a straight line segment, thereby providing skewed magnetic field strength.

[012] In another embodiment of the invention, area of the magnet on one side of the straight line segment has the first polarity and area of the magnet on other side of the straight line segment has the second polarity.

[013] In a further embodiment of the invention, angle between the base edge and the hypotenuse edge of the fifth region is equal to angle between the base edge and the hypotenuse edge of the sixth region, and ranges between 15-25 degrees.

[014] In a further embodiment of the invention, the first region has a right-angled triangular shaped seventh region with the second polarity disposed at an end of the first region, such that a hypotenuse edge of the seventh region is parallel and equal in length to the hypotenuse edge of the sixth region. [015] In another embodiment of the invention, the third region has a right-angled triangular shaped eighth region with the first polarity disposed at an end of the third region, such that a hypotenuse edge of the eighth region is parallel and equal in length to the hypotenuse edge of the fifth region. [016] In a further embodiment of the invention, the seventh region has the second polarity, area of the magnet defined between the hypotenuse edge of the seventh region and the straight line segment has the first polarity, area of the magnet defined between the straight line segment and the hypotenuse edge of the eight region has the second polarity, and the eight region has the first polarity, thereby providing skewed magnetic field strength. [017] In another aspect, the present invention relates to rotary electric machine having a stator having a plurality of stator teeth for stator windings, and a rotor having a plurality of magnets disposed facing the stator. Each magnet has a first region with a first polarity, a second region with the first polarity such that the first region and the second region are adjacent to each other, a third region with a second polarity such that the third region and the second region are connected by a fifth region with the second polarity. Further, each magnet has a fourth region with the second polarity such that the fourth region is adjacent to the third region and the fourth region is connected to the first region by a sixth region with the first polarity. Herein area of the second region is lower than area of the first region and area of the fourth region is lower than area of the third region, thereby providing a skewed magnetic field strength.

[018] In an embodiment of the invention, the first region and the third region have a rectangular shape, the second region and the fourth region have a trapezoidal shape, and the fifth region and the sixth region have a right-angled triangular shape, when viewed from a centre of the rotor.

[019] In a further embodiment of the invention, angle between a base edge and a hypotenuse edge of the fifth region is equal to angle between a base edge and a hypotenuse edge of the sixth region, and ranges between 15-25 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

[020] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Figure 1 illustrates an exemplary rotary electric machine, in accordance with an embodiment of the invention. Figure 2 illustrates a sectional view of the rotary electric machine, in accordance with an embodiment of the invention.

Figure 3 illustrates an exploded view of the rotary electric machine, in accordance with an embodiment of the invention.

Figure 4a, 4b, 4c and 4d illustrates a front view, a side view, a perspective view and a top view of the rotor respectively, in accordance with an embodiment of the invention.

Figure 5 illustrates a magnet of the rotor when viewed from a centre of the rotor, in accordance with an embodiment of the invention. Figure 6 illustrates the magnet of the rotor, in accordance with an embodiment of the invention.

Figure 7 illustrates the magnet of the rotor, in accordance with an embodiment of the invention. Figure 8 illustrates the arrangement of skewed polarity on the magnets in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[021] The present invention relates to a rotary electrical machine. In particular, the present invention relates to a rotor for a rotary electrical machine with reduced torque ripple and reduced noise.

[022] Figure 1 illustrates an exemplary rotary electrical machine 10. As illustrated, the rotary electric machine 10 comprises a rotor 20 and a stator 30 (shown in Figure 3). In the embodiment depicted in Figure 1 , the rotary electric machine 10 is configured for functioning as at least a generator in a vehicle for charging a battery of the vehicle. The rotary electric machine 10 is coupled to an engine of the vehicle.

[023] Figure 2 illustrates a sectional view of the exemplary rotary electric machine 10 and Figure 3 illustrates an exploded view of the rotary electrical machine 10. As illustrated in Figure 2, the stator 30 of the electric machine is mounted on the crankcase 40. Further, the rotor 20 of the electric machine 10 is coupled to the engine by means of a crankshaft 50. Rotation of the engine, and hence the crankshaft 50 causes the rotor 20 to rotate. The stator 30 comprises a plurality of stator teeth that receive stator windings. The rotor 20 comprises of a plurality of magnets 100 arranged adjoining each other so as to complete a cylinder like structure of the rotor 20. The plurality of magnets 100 have an associated magnetic field and magnetic field strength. The plurality of magnets 100 are arranged facing the stator 30 so that the rotation of the plurality of magnets 100 of the rotor 20 results in rotation of the associated magnetic field, generating a current in the stator winding on the stator 30.

[024] The plurality of magnets 100 are arranged such that the polarity of the plurality of magnets 100 has a configuration in which a first polarity, say north pole of one magnet is arranged adjoining a second polarity, say south pole of a second magnet, the second polarity of the second magnet is arranged adjoining the first polarity of a third magnet and so on.

[025] As seen in Figures 4a-4d, and more particularly Figure 4a, the plurality of magnets 100 have an arcuate cross section when seen in a front view. Further, each magnet 100 will accordingly have an inner curved surface area facing inwards towards the stator 30 and an outer curved surface area. It thus becomes evident that, when seen from a centre of the rotor 20, the inner curved surface area of each of the magnets 100 will have a substantially planar and rectangular shape. The substantially rectangular shape of the inner curved surface area of each magnet 100 as aforementioned, has been illustrated in Figure 5.

[026] Figure 6 further illustrates the inner curved surface area of each magnet 100. As illustrated, each magnet has a first region 110 having the first polarity, say north pole and a second region 120 with the first polarity such that the first region 110 and the second region 120 are adjacent to each other. The magnet 100 further comprises of a third region 130 having a second polarity, say south pole such that the third region 130 and the second region 120 are connected by a fifth region 150 with the second polarity.

[027] The magnet 100 further has a fourth region 140 with the second polarity such that the fourth region 140 is adjacent to the third region 130 and the fourth region 140 is connected to the first region 110 by a sixth region 160 with the first polarity. Herein, as can be seen in Figure 6, area of the second region 120 is lower than area of the first region 110 and area of the fourth region 140 is lower than area of the third region 130. Such a configuration of polarities on the magnet 100 provides a magnet 100 wherein the first region 110, the second region 120 and the sixth region 160 combined correspond to the first polarity, and the third region 130, the fourth region 140 and the fifth region 150 combined correspond to the second polarity. Such a configuration of opposing polarities on the magnet 100 thereby provides a skewed magnetic field strength, as opposed to the conventional arrangement of symmetrical and linear configuration.

[028] Such a skewed arrangement of opposing polarities on the magnet 100 results in reduction of magnetic field strength around the edges of the magnet 100 in comparison to the centre of the magnet 100, leading to reduction in rate of change of magnetic field. This reduction leads to lower torque ripple and hence reduced noise.

[029] As can be seen in the embodiment depicted in Figure 6, the first region 110 and the third region 130 have a rectangular shape. Further, the second region 120 and the fourth region 140 have a trapezoidal shape and the fifth region 150 and the sixth region 160 have a right-angled triangular shape, when viewed from the centre of the rotor. As further illustrated in Figure 6, a base edge (OX’) of the fifth region 150 is adjacent to the third region 130. A hypotenuse edge (OA’) of the fifth region 150 is adjacent to the second region 120. Furthermore, a base edge (OX) of the sixth region 160 is adjacent to the first region 110 and a hypotenuse edge (OA) of the sixth region 160 is adjacent to the fourth region 140.

[030] As can be further seen in Figure 6, area of the first region 110 is equal to area of the third region 130, area of the second region 120 is equal to area of the fourth region 140, and area of the fifth region 150 is equal to area of the sixth region 160. Therefore, the combined area of the first region 110, the second region 120 and the sixth region 160 corresponding to the first polarity is equal to the combined area of the third region 130, fourth region 140 and the fifth region 150 corresponding to the second polarity. [031] As can be further seen in the Figure 6, the hypotenuse edge (OA’) of the fifth region

150 and the hypotenuse edge (OA) of the sixth region 160 join in a straight line segment (AA’). Herein, area of the magnet 100 on one side of the straight line segment (AA’) has the first polarity and area of the magnet 100 on other side of the straight line segment (AA’) has the second polarity. Such a configuration of the polarities in the magnet 100 provides for a magnet 100 wherein the line of division between the opposing polarities is skewed with respect to the edges of the magnet 100, and hence provide a skewed magnetic field. [032] It is to be noted that as the skewing of the polarities in the magnet 100 is increased, the electrical losses increase with it. To address this, in an embodiment, angle between the base edge (OX’) and the hypotenuse edge (OA’) of the fifth region 150 is equal to angle between the base edge (OX) and the hypotenuse edge (OA) of the sixth region 160, and ranges between 15-25 degrees. The maintaining of this angular range of skewing between 15 to 25 degrees leads to the electrical losses being maintained within an optimum range. [033] Figure 7 illustrates another configuration of magnet polarities in the magnet 100 of the rotor 20. As illustrated in the embodiment depicted in Figure 7, the first region 110 further comprises a right-angled triangular shaped seventh region 170 with the second polarity disposed at an end of the first region 110, such that a hypotenuse edge (BB’) of the seventh region 170 is parallel and equal in length to the hypotenuse edge (OA) of the sixth region 160. In addition, the third region 130 further comprises a right-angled triangular shaped eighth region 180 with the first polarity disposed at an end of the third region 130, such that a hypotenuse edge (CC’) of the eighth region 180 is parallel and equal in length to the hypotenuse edge (OA’) of the fifth region 150. In this embodiment, the seventh region 170 has the second polarity, area of the magnet 100 defined between the hypotenuse edge (BB’) of the seventh region 170 and the straight line segment (AA’) has the first polarity, area of the magnet 100 defined between the straight line segment (AA’) and the hypotenuse edge (CC’) of the eight region 180 has the second polarity, and the eight region 180 has the first polarity. This configuration provides small regions of opposing polarity at the end of the first region 110 and the end of the third region 130 as illustrated in

Figure 8. As a result, magnetic field strength at ends of the magnet 100 is further reduced. Thus, even though actual field strength of the magnet 100 is sufficiently high, since the edge, and specifically the ends of the magnet 100 has lower magnetic field strength, the rate of change of magnetic field is reduced. This leads to reduction in the torque ripple and hence the reduction in noise.

[034] In another aspect, the present invention relates to a rotary electric machine 10 comprising a stator 30 having a plurality of teeth for stator windings, and a rotor 20 having the plurality of magnets 100 as explained hereinbefore. [035] Advantageously, the present invention provides for a rotor for a rotary electric machine which has reduced torque ripple and hence reduced noise, while not compromising with the voltage generation capacity of the rotary electric machine.

[036] Further, the present invention allows for the provision of a skewed arrangement of polarity in the magnets of the rotor, while not excessively increasing the electrical losses. [037] Furthermore, the present invention provides a rotary electric machine which can achieve reduced torque ripple and noise without an increase in the number of magnets and is therefore less cost intensive and easier to manufacture.

[038] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.