Technical field

The present application relates to the technical field of electric machines, in particular to a rotor having an improved structure and an electric machine comprising such a rotor.

Background art

Electric machines have achieved widespread use as devices for converting electrical energy to mechanical energy, for example in electric vehicles. Existing electric machines generally comprise a rotor and a stator, and are divided into several types based on the way in which the magnetic field and electric field interact between the rotor and stator, etc. Since the magnetic field will cause "hysteresis loss" and "eddy current loss" in the conductors of the rotor and stator (e.g. windings or core), both the rotor and stator of the electric machine will generate a large amount of heat during operation.

Electric machines can dissipate heat by natural cooling, forced air cooling or liquid cooling, but in actual application environments, the electric machine is often partially covered or blocked by other components, affecting air circulation, orthere is variation in local cooling medium temperatures in the electric machine; this has an impact on the heat dissipation result, leading to local overheating. For example, a naturally cooled electric machine for an electric vehicle achieves heat dissipation by natural convection at a housing and two end cover surfaces, but due to limitations of vehicle chassis installation space, blocking by other components (e.g. car beams, controllers, cables, etc.) might occur at certain axial positions of the electric machine. In such a layout, if unobstructed circulation of air is not possible at the housing surface, a temperature distribution imbalance may occur in the rotor and stator in the electric machine, in the direction of the longitudinal axis. As another example, in the case of electric machines with forced air cooling or liquid cooling, the cooling result is better at a position close to an air (liquid) intake because the medium is at a lower temperature at the air (liquid) intake, while the cooling result is worse at a position close to an air (liquid) outlet because the medium is at a higher temperature at the air (liquid) outlet. Furthermore, since there is often an interference fit between the stator and housing, the heat of the stator can dissipate promptly through the electric machine casing, whereas the heat of the rotor will diffuse outwards more slowly, resulting in heat accumulation. If the axial length of the rotor of the electric machine is greater, this imbalance will be exacerbated. This kind of local overheating restricts the maximum electrical load that the electric machine can tolerate, resulting in loads that are far smaller than the designed peak torque, and may even lead to electric machine burnout.

Thus, there is a need to make improvements to existing electric machines, in order to mitigate rotor temperature imbalance, and avoid local overheating in electric machines, so as to further increase the load-bearing capability of electric machines.

Summary of the invention

An object of the present application is to propose a rotor having an improved structure and an electric machine comprising such a rotor, with the aim of overcoming the technical problems mentioned above.

To this end, according to one aspect of the present application, a rotor for an electric machine is provided, comprising: a rotor body, configured to be connectable to a shaft of the electric machine in a fixed manner, the rotor body having a longitudinal axis, wherein the rotor body has a varying cross section at different positions along the longitudinal axis.

Optionally, the rotor further comprises multiple permanent magnets embedded in the rotor body.

Optionally, the multiple permanent magnets are arranged such that the geometric centres thereof are at the same radial distance from the longitudinal axis of the rotor body.

Optionally, the rotor body is made of stacked iron alloy sheets having different dimensions.

According to another aspect of the present application, an electric machine is provided, comprising: a stator, provided with a chamber; the rotor as described above, the rotor being accommodated in the chamber of the stator; and a shaft, connected to the rotor body in a fixed manner.

Optionally, the chamber of the stator has a varying cross section at different positions along the longitudinal axis of the rotor.

Optionally, the electric machine further comprises a housing; a large- diameter part of the rotor body is disposed in a position corresponding to a part of the housing where heat dissipation conditions are favourable, and a small- diameter part of the rotor body is disposed in a position corresponding to a part of the housing where heat dissipation conditions are not favourable.

Optionally, the electric machine further comprises a cooling fan; a large- diameter part of the rotor body is disposed close to the cooling fan, and a small- diameter part of the rotor body is disposed remote from the cooling fan.

Optionally, the electric machine further comprises a liquid cooling circuit; a large-diameter part of the rotor body is disposed close to a liquid inlet of the liquid cooling circuit, and a small-diameter part of the rotor body is disposed close to a liquid outlet of the liquid cooling circuit.

In the rotor and the electric machine comprising such a rotor according to the present application, the heat distribution of the rotor can be improved by configuring the rotor to have a varying cross section in the direction of the longitudinal axis, thereby mitigating the imbalance in rotor temperature, and ensuring safe and efficient operation of the electric machine.

Brief description of the drawings

Demonstrative embodiments of the present application will be described in detail below with reference to the drawings. It should be understood that the embodiments described below are merely intended to explain the present application, without limiting the scope thereof. In the drawings:

Fig. 1 is a cross-sectional drawing which shows schematically an electric machine according to an embodiment of the present application.

Fig. 2A is a perspective view which shows schematically a rotor of the electric machine in fig. 1.

Fig. 2B is a perspective view which shows schematically a stator of the electric machine in fig. 1.

Figs. 3A and 3B are drawings of cross sections taken at a large-diameter part and a small-diameter part of the rotor respectively, and show schematically the electric machine in fig. 1.

Detailed description of the invention

Preferred embodiments of the present application are described in detail below with reference to examples. In the embodiments of the present application, a rotor comprising permanent magnets, and a permanent magnet electric machine, are taken as examples to describe the present application. Flowever, those skilled in the art should understand that these demonstrative embodiments do not signify any limitation of the present application. In addition, in the absence of conflict, features in embodiments of the present application may be combined with each other. In different drawings, identical or similar components are indicated by identical reference labels, and in the interests of conciseness, other components are omitted, but this does not indicate that the rotor and electric machine of the present application cannot include other components. It should be understood that component sizes, proportional relations and component quantities in the drawings are not limitations on the present application.

As shown in fig. 1, an electric machine 100 according to an embodiment of the present application substantially comprises a rotor 20, a stator 30 and a shaft 40. The rotor 20 comprises a rotor body 21, the rotor body 21 being configured to be connectable to the shaft 40 in a fixed manner. For example, the shaft 40 may pass through a centre hole 23 of the rotor body 21, and be connected in a fixed manner to the rotor body 21 by means of a key or in another way. The rotor body 21 has a longitudinal axis X, and correspondingly has a longitudinal length extending along the longitudinal axis X. The stator 30 is provided with a chamber 31, and the rotor 20 can be accommodated in the chamber 31 of the stator 30. Furthermore, the electric machine 100 may further comprise a housing 10, a first end cover 11 and a second end cover 12; a space for accommodating the rotor 20 and stator 30 is defined by the housing 10 together with the first end cover 11 and second end cover 12. One end of the shaft 40 may extend out through the first end cover 11, for connection to a transmission apparatus (not shown). Of course, the electric machine 100 may also comprise other components, e.g. bearings, bolts, conductive wires, etc., but these are not described further here.

As shown in figs. 1 and 2A, in the electric machine 100 of the present application, a cross section of the rotor 20 varies at different positions along the longitudinal axis X, and is not constant as in the prior art. Specifically, the rotor body 21 may have a varying cross section at different positions along the longitudinal axis X thereof. In other words, the rotor body 21 may have different cross sections in different planes perpendicular to the longitudinal axis X. In the case where the rotor body 21 is rotationally symmetric relative to the longitudinal axis X, the rotor body 21 may have different outer diameters in the direction of the longitudinal axis X. Thus, by configuring the rotor body 20 to have a varying cross section at different positions on the longitudinal axis X, the heat distribution of the rotor 20 can be improved. Correspondingly, the stator 30 may also have a varying cross section at different positions on the longitudinal axis X, in order to maintain conformity with the varying cross section of the rotor 20 and maintain a small gap, as shown in figs. 1 and 2B. Furthermore, the stator 30 may further comprise wire grooves 32, to accommodate excitation windings.

A permanent magnet electric machine is taken as an example below to further describe the improvement brought about by the variation in cross- section of the rotor 20.

In the case of a permanent magnet electric machine, as shown in fig. 2A, the rotor 20 may further comprise multiple permanent magnets 22; the multiple permanent magnets 22 may be embedded in the rotor body 21. In general, the permanent magnets 22 are arranged such that the geometric centres thereof are at the same radial distance from the longitudinal axis X of the rotor body 21, i.e. uniformly distributed in the rotor body 21 in an annular fashion around the longitudinal axis X. It should be pointed out that in addition to the V-shaped arrangement of the permanent magnets 22 shown in fig. 2A, other arrangements may also be used accordingto the shape of the magnets, the number of magnetic pole pairs, the direction of the magnetic field, etc. The permanent magnets 22 may be ferrite magnets or rare earth magnets, etc. which are widely used in the field; the rotor body 21 may be made of stacked iron alloy sheets having different dimensions, i.e. a core.

In the course of operation, the flow of magnetic flux of the permanent magnets 22 in the rotor body 21 will generate heat, i.e. so-called "hysteresis loss". Furthermore, since the rotor body 21 is itself a conductor too, an induced emf will arise in a plane perpendicular to magnetic force lines, with the formation of a closed circuit in a cross section of the rotor body 21 and the generation of current, causing the rotor body 21 to heat up, i.e. so-called "eddy current loss". If the position of each permanent magnet 22 embedded in the rotor body 21 relative to the longitudinal axis X is constant, the permanent magnet 22 will be at different distances from an outer surface of the rotor body 21, due to the fact that the cross section of the rotor body 21 of the rotor 20 varies at different positions along the longitudinal axis X. As shown in fig. 3A, at a large-diameter part of the rotor body 21, the distance between the permanent magnet 22 and the outer surface of the rotor body 21 is greater, and the rotor body 21 correspondingly has a greater material thickness at this position. In this case, the path of circulation of magnetic flux in the rotor body 21 is longer, resulting in greater "hysteresis loss", and at the same time, the induced emf will form a larger closed circuit in the rotor body material of larger cross section, resulting in greater "eddy current loss". Thus, the rotor body 21 of the rotor 20 will generate more heat, centred at the permanent magnet 22, at the large-diameter part, resulting in a higher temperature here, and since the permanent magnet 22 is at a greater distance from the outer surface of the rotor body 21, the rate of outward diffusion of heat will be correspondingly slower. Taking together the factors influencing heat generation and heat diffusion, it is clear that the temperature of the rotor 20 is higher at the large-diameter part. Conversely, as shown in fig. 3B, at a small-diameter part of the rotor 2, the distance between the permanent magnet 22 and the outer surface of the rotor body 21 is smaller, and the heat and temperature situations are correspondingly opposite to those described above.

Thus, in the design of the rotor 20, the large-diameter part of the rotor body 21 may be disposed in a position corresponding to a part of the housing 10 where heat dissipation conditions are favourable, and the small-diameter part of the rotor body 21 may be disposed in a position corresponding to a part of the housing 10 where heat dissipation conditions are not favourable. It should be pointed out that figs. 1 to 2B merely show an example of a naturally air-cooled electric machine, and the form of variation of the rotor 20 and stator 30 shown in the direction of the longitudinal axis is merely schematic; in an actual electric machine, they may vary according to the heat dissipation situation and structural requirements, etc. of the electric machine at different positions. Thus, the rotor 20 of the present application is not limited to the shape and structure shown in figs. 1 - 2B.

Furthermore, the electric machine 100 may also be an electric machine with forced air cooling, and correspondingly comprise a cooling fan (not shown), mounted at one end of the electric machine 100 for example; moreover, the large-diameter part of the rotor body 21 may be disposed close to the cooling fan, and the small-diameter part of the rotor body 21 may be disposed remote from the cooling fan. Alternatively, the electric machine 100 may also be an electric machine with forced liquid cooling, and correspondingly comprise a liquid cooling circuit (not shown), e.g. a cooling liquid circuit surrounding the housing 10 or embedded in the housing 10; moreover, the large-diameter part of the rotor body 21 may be disposed close to a liquid inlet of the liquid cooling circuit, and the small-diameter part of the rotor body 21 may be disposed close to a liquid outlet of the liquid cooling circuit.

Thus, by designing the rotor 20 to have a varying cross section along the longitudinal axis X of the rotor body 21, heat generation and loss in the axial direction of the rotor 20 can be regulated so as to match actual heat dissipation conditions, such that the temperature of the rotor 20 of the electric machine is balanced overall, avoiding local overheating, and the power density of the electric machine can thereby be increased.

Of course, based on magnetic field design requirements, etc., the permanent magnets 22 may also be arranged to be at different radial distances from the longitudinal axis X of the rotor body 21. In this case, the heat distribution of the rotor 20 can likewise be adjusted by adjusting the cross section of the rotor 20 at different positions on the longitudinal axis X, thereby improving the heat dissipation situation of the electric machine; this will not be described further here.

Although the principles of the present invention have been explained above by taking a rotor comprising permanent magnets and a permanent magnet electric machine as examples, in the case of any electric machine using the principle of electromagnetic induction to achieve the conversion of electrical energy and mechanical energy, as long as there is heat generation due to "hysteresis loss" and/or "eddy current loss" in the rotor and/or stator, and heat dissipation conditions are limited, the cross section of the rotor can be varied in accordance with the principles of the present invention to match the heat dissipation conditions, mitigating the temperature imbalance in the electric machine, avoiding local overheating in the electric machine, and thereby further increasing the load-bearing capability of the electric machine.

The present application has been described in detail above with reference to particular embodiments. Clearly, all of the embodiments described above and shown in the drawings should be understood to be demonstrative, without limiting the present application. For example, the present application has been described in preferred embodiments by taking a permanent magnet electric machine and a rotor thereof as examples, but a person skilled in the art could make various alterations or amendments thereto without departing from the spirit of the present application, all such alterations or amendments falling within the scope of the present application.