Patent Application
20230291289
The present invention relates to rotor assemblies of high efficiency motors, and more specifically to rotor assemblies with selectively nitride laminations to reduce flux.
Reducing the flux loss to increase the motor efficiency or increase the output of the motor without increasing the size of the motor is an ongoing challenge for electric and hybrid vehicles.
In a rotating electric machine, alternating current (AC) power is supplied to stator windings, to generate a rotating magnetic field. As the stator of such a rotating electric machine, there is a known structure in which terminals of segment coils are welded and connected. Coils are wound around a stator. A rotating electric machine supplies AC power to the coils, to cause the coils to generate a rotating magnetic field. A rotor is rotated by this rotating magnetic field to produce mechanical output power. Also, the mechanical energy applied to the rotor can be converted into electric energy, and AC power can be output from coils of the stator winding. In this manner, the rotating electric machine functions as an electric motor or a generator.
Conventionally, the motor laminations of the rotor are made of steel that has an insolation coating (C5).
According to one embodiment of the present invention, targeted nitriding is added to specific spots to decrease flux in bridge areas of motor steel laminations to alter the electromagnetic properties of these areas to reduce flux loss and increase the efficiency by using insulations coatings on the lamination steels as a nitriding barrier. The reduction in flux allows for the use of smaller magnets, which decreases costs and results in an increase in performance.
According to another embodiment of the present invention, a method to reduce the flux loss in motor laminations is disclosed. In a first step, insulation coating is locally removed in the desired areas during the lamination forming process. Next, laminations are nitrided to achieve selectively nitriding local areas in separated lamination configurations or stacked in a nitriding heat treating furnace.
Motor laminations form the core of an electric motor's stator and rotor as shown in
More specifically, bridge region 111 is between the outer circumferential edge 100a and a first magnet slot 103. Bridge region 107 is between the outer circumferential edge 100a and a second magnet slot 104. Bridge region 108 is between the outer circumferential edge 100a and the fourth magnet slot 106. Bridge region 109 is between the third magnet slot 105 and the fourth magnet slot 106. Bridge region 110 is between the outer circumferential edge 100a and the third magnet slot 105. Between the first and the second magnet slots 103, 104 is bridge region 112. The bridge region thickness should be as small or thin as possible while still maintaining the structural integrity of the rotor during operation of the motor.
The layout of the magnet slots 103-106 is an example and can be altered within the scope of the art. For example, an additional magnet slot 115 can be present between the first magnet slot 103 and second magnet slot 104 as shown in
The magnets slots 103-106 are preferably as far radially outward as possible for a given rotor outer diameter (e.g. away from the outer circumference 100a) to maximize torque production of the motor, as torque equals force times distance. Therefore, the further out the slots 103-106, the greater the distance, and the more torque for a given force. The reaction between the magnets 125 within the magnet slots 103-106 and the magnetic field generated in the stator 150 create the force. It is noted that there is a relationship between the magnet slot 103-106 placement within the rotor lamination 10 for a given rotor outer diameter 100a and the structural strength at the bridge regions 107-112 between the magnet slots 103-106 to keep the rotor lamination 10 from breaking.
Embodiments of the present invention reduce magnetic flux leakage through the lamination of bridge regions 107-113 while maintaining the structural integrity of the lamination to improve power density.
In one embodiment, the bridge regions 107-113 of the rotor laminations undergo cold working. Some or all of the bridge regions can undergo cold working. The amount of bridge regions 107-113 which undergo cold working can vary depending on the application and the amount of flux to be focused through the magnets 125 of the magnet slots 103-106. The more bridge regions 107-113 which receive cold working, the more flux focused through the magnets 125 of the magnet slots 103-106.
Cold working strengthens metal by changing its shape without the use of heat and more specifically, is conducted at temperatures below the metal's recrystallization point by applying mechanical stress. Subjecting the metal to the mechanical stress causes a permanent change to the metal's crystalline structure, causing an increase in strength. The cold work is preferably coining, although other types of cold working can be used. For example, cold working can take place in a progressive stamping tool or as a subsequent process. If the cold working occurs within the progressive stamping tool, the cold working of the rotor laminations 10 takes place either before or after the magnet slots 103-106 are produced. For example, cold working of the rotor lamination 10 prior to forming of the magnet slots 103-106 would require removing a portion of the cold worked area after the magnet slots 103-106 are stamped.
In another embodiment, the bridge regions 107-113 are nitrided. Nitriding is a heat-treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. Nitriding can either be carried out on the finished laminated stack forming the rotor 130 or on the individual laminations 10.
Selective nitriding in an embodiment of the present invention nitrides the bridge areas 103-113 of motor steel laminations to alter the electromagnetic properties of the areas to reduce the flux loss and increase the efficiency by using the insulation coatings or modified insulation coatings on the lamination steels as a nitriding barrier. The commonly used insulation coating C5 on the commercial lamination steels or modification coating acts as a nitriding barrier that prevent the steel underneath to be nitrided, while the surfaces where the coating is removed or not coated will be nitrided, in return reduced the magnetic properties of the lamination steel. Nitriding with the coating on the lamination does not change the magnetic properties. Thus, reducing the flux loss in motor laminations is achieved by locally removing the insulation coating in the desired areas during lamination forming process, then the laminations are nitrided to achieve selectively nitriding local areas either in separated lamination configuration or stacked in a nitriding heat treating furnace. In other words, the nitriding is specific areas force the flux to travel through the magnets 125.
In another embodiment, the bridge regions 107-113 are cold worked and then nitrided.
In yet another embodiment, individual rotor lamination segments are each comprised of a plurality magnet slot grouping pieces 162 which are individually constructed and pieced together to form a singular, circular, rotor lamination. The plurality of magnet slot grouping pieces 162 can be interconnected by a lock and key or dovetail assembly of pins 151a, 151b and sockets 152a, 152b. Pin 151a, adjacent the outer circumferential edge 100a can be received within a socket 152a of an adjacent individual magnet slot grouping piece 162 and the pin 151b, adjacent the inner circumferential edge 100b can be received within a socket 152b of an adjacent individual magnet slot grouping piece 162. By crafting individual rotor lamination segments, less waste material is generated and small die sets can be used. An example of an individual rotor lamination segment is shown in
In yet another embodiment, the insert pieces 202, 203 could be by non-magnetic and nitriding can be applied to the insert pieces areas of the single rotor lamination to additionally force the flux to travel through the magnet 262.
Manufacturing
The rotor laminations are each produced by progressive stamping of steel slit coil which is automatically fed into a progressive die.
Cold working can take place in a progressive stamping tool or as a subsequent process. If the cold working occurs within the progressive stamping tool, the cold working of the rotor laminations 10 takes place either before or after the magnet slots 103-106 are produced. For example, cold working of the rotor lamination 10 prior to forming of the magnet slots 103-106 would require removing a portion of the cold worked area after the magnet slots 103-106 are stamped.
The entire circumference of the rotor lamination can be created through the progressive stamping as single rotor lamination or alternatively pieces comprising the circumference of the single rotor lamination can be created and pieced together after stamping to form the single rotor lamination. For example,
After the completed rotor lamination parts are removed from the progressive die, the parts are cleaned and dried.
Nitriding can either be carried out on the finished laminated stack forming the rotor 130 or on the individual laminations 10.
At least some of the rotor laminations are aligned and adhered together. The adherence of the single rotor laminations together can take place though various means, for example by adhesives, welding, mechanical fit, interlocking etc . . . .
To test the effectiveness of the cold working or nitriding the bridge regions of the rotor laminations, a wind toroid and test base-line toroid were constructed. Magnetic flux density testing was performed. Direct current (DC) was conducted through a first toroid without nitriding or coating, a second toroid with nitriding and a coating, such as C5, and a third toroid with nitriding, but no coating. As shown in
Alternating current (AC) was also conducted through the first toroid without nitriding or coating, a second toroid with nitriding and a coating, such as C5, a third toroid with nitriding, but no coating, and a fourth toroid with cold working up to 200 Hertz (Hz). As shown in
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.
