Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-09-28
2004-04-13
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S216006, C310S216055
Reexamination Certificate
active
06720702
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application, Serial No. 101 26 340.6, filed May 30, 2001, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates, in general, to an electric machine, and more particularly, to an electric machine of a type having a rotor, a shaft, a structure for excitation of at least parts of the rotor, a torque receiving structure upon the rotor, and a structure for realizing a force transfer between rotor and shaft.
Electric machine with rotors are known having at least one structure for excitation of at least parts of the rotor in order to impart a torque of the rotor and to thereby cause a rotation of the rotor together with the shaft. Excitation may be realized in various ways. Examples include the provision of current-carrying conductors, configured as winding, or the use of permanent magnets that effect a permanent excitation. Suitably, current-carrying conductors are placed in slots of the rotor. Forces applied upon at least one of the current-carrying conductors can, for example, be so transmitted to at least one side of the slot that torque-forming forces can act also on the entire rotor. The permanent magnets as well as the electric conductors are situated on the outer side of the rotor, whereby the permanent magnets may be attached, e.g., by gluing, to the outer surface area of the rotor. This material-based joint between the outer surface area of the rotor and the permanent magnets allows transfer of forces, in particular of torque. Typically, the rotor is also wrapped on the outside by a bandage, whereby the bandage is able to absorb centrifugal forces and holds the permanent magnets upon the outer surface area of the rotor.
An excitation structure, which is situated on the rotor, becomes part of the rotor. Suitably, the excitation structure is located on the rotor component which is preferred to conduct the magnetic flux in the rotor. This region is normally designed as annulus, i.e. flux guide ring or partial ring, and is able to receive the excitation structure. Furthermore, this ring-shaped component itself is also able to receive torques from the excitation structure and thus constitutes the torque receiving structure upon the rotor. The structure for receiving a force and/or torque upon the rotor may include a non-positive engagement, a positive engagement, or a material based joint, whereby these types of connections have the effect to make the excitation structure as part of the rotor. Positive connections include, for example, slots in the rotor for receiving the excitation structure, e.g. a winding. An example of a material-based joint includes the gluing of permanent magnets onto an outer radius of the rotor, whereby a bandage may additionally secure the permanent magnets.
Forces exerted upon the excitation structure are directed via the rotor to an interface with the shaft, so as to transfer forces to the shaft. The structure for force transfer between rotor and shaft defines this interface. Examples for a force-transfer structure include fitting keys or material-based joints, realized, for example, by welding, as well as non-positive engagement, realized, for example, through shrinkage. The force transfer and torque transfer between the torque receiving structure upon the rotor and the interface between rotor and shaft is implemented by the material of the rotor therebetween. Normally, the rotor of electric machines is made from punched laminations placed sequentially.
The conventional process for implementing a force transfer between a flux-conducting outer region of the rotor and the interface to the shaft suffers shortcomings because the force transfer is realized across solid rotor material or across rotor material formed with round bores or recesses. The moment of inertia of a body, especially of a rotating body increases, as the body mass increases, in particular of the outer regions. Thus, a solid configuration or at least mostly solid configuration of the rotor results in a significant moment of inertia of such a rotor.
It would therefore be desirable and advantageous to provide an improved electric machine to obviate prior art shortcomings and to include a rotor of low inertia.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an electric machine includes a rotor, a shaft, an excitation structure for generating a torque, a torque receiving structure for receiving the torque from the excitation structure, a structure for force transfer between the rotor and the shaft, and a web structure, disposed between the torque receiving structure and the force transfer structure, to effect an inertial mass relief of the rotor.
The present invention resolves prior art problems by realizing an inertial mass relief through provision of webs so that the moment of inertia of the rotor is reduced. The webs may have a secant-like configuration, and/or arcuate configuration and/or curved configuration. The dynamics of an electric machine can be increased by implementing a higher power output or by changing the moment of inertia of moving parts. The shaft as well as the rotor constitute moving parts of an electric machine and both rotate about the same rotation axis. As the moment of inertia of a rotary system increases with increase in distance of a mass from the rotation axis, the moment of inertial of an electric machine is reduced by decreasing the moment of inertia of the rotor because, compared to the shaft, the rotor has masses which rotate at a greater distance to the rotation axis. Although punching holes in rotor laminations of a laminated rotor had been proposed, these holes were limited to a central radius zone of the rotor, because the outer region (area of great to maximum radii) of the rotor formed a ring for conducting the magnetic flux, and the inner region (area of small to minimum radii) of the rotor formed the structure to transfer torques and forces to the shaft. Force transfer can be realized in various ways, such as, e.g., tongue and groove joints, representing a positive engagement, or non-positive engagement through shrink-on operation, or material-based joint through welding or gluing or other suitable ways.
Force transfer and/or torque transfer from the torque receiving structure upon the rotor to the structure for force transfer onto the shaft can be realized through interconnection via secant-like and/or arcuate webs. The term “secant” denotes a straight line and/or segment which intersects a curve or a circle at two points. Secant-like webs denote webs that at least partially conform to the configuration of such secants. Compared to straight lines and/or segments, secant-like webs are three-dimensional, whereby the space directions are variable. The webs may also have an arcuate configuration and assume similar or same tasks as secant-like webs. Curved secant-like webs can hereby be considered also as arcuate webs. Secant-like webs and/or arcuate webs can be so configured as to be able to transfer at least maximum torques and forces while taking into account the fatigue factor of the material associated with fabrication of the webs. When establishing a web pattern within a rotor for transfer of forces and/or torques, apart from the torque receiving structure upon the rotor and the structure for torque transfer to the shaft, and also the region of the flux pattern, all other areas of the rotor can be used for mass relief and material removal. As a consequence, substantial areas of the rotor are involved here and do not require original rotor material. The material reduction and thus the rotor mass relief decreases the moment of inertia and increases the dynamics of the electric machine.
The rotor may be made of one or more materials. Laminated rotors include mainly a plurality of rotor laminations stacked sequentially. Rotor laminations can easily be made and suitably configured in a cost-efficient manner through a punching process. Also, webs can easily be punch
Feiereisen Henry M.
Lam Thanh
Siemens Aktiengesellschaft
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