Permanent-magnet rotor shrink-fit assembly

Details Permanent-magnet rotor shrink-fit assembly Permanent-magnet rotor shrink-fit assembly

1986-10-27

1987-09-29

Salce, Patrick R.

Electrical generator or motor structure

Dynamoelectric

Rotary

310 42, 310261, 29598, H02K 1502, H02K 2114

Patent

active

046971149

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to a permanent-magnet rotor assembly and, more specifically, to improvements in a fastening structure for fastening end plates to the rotor shaft of a permanent-magnet rotor assembly.
2. Background Art
Generally, a permanent-magnet rotor assembly comprises a rotor shaft, a plurality of yokes extending along the axis of the rotor shaft and arranged around the rotor shaft at circumferential intervals, permanent magnets each being held between the two adjacent yokes, and a pair of end plates attached to the opposite ends of the yokes and fastened to the rotor shaft, respectively.
In such a permanent magnet rotor assembly, the end plates are placed in contact with the yokes and the permanent magnets, and are fastened to the opposite ends of the yokes, respectively, with stud bolts or fastening bolts penetrating the yokes. Therefore, the end plates must be formed of a nonmagnetic material, such as a stainless steel, to prevent a short-circuiting of the magnetic paths through the end plates.
On the other hand, the end plates must be firmly secured to the rotor shaft. Accordingly, it has been a conventional practice to form an end plate integrally with a boss having a large wall thickness, by casting and/or machining and to secure the end plate to a rotor shaft by fitting the rotor shaft in the boss by a shrinkage fit. However, since nonmagnetic materials, in general, are expensive, forming an end plate integrally with a boss having a large wall thickness of a non-magnetic material is very costly.
It is possible to secure an end plate having a boss having a small wall thickness and formed of a nonmagnetic material to a rotor shaft by welding the boss to the rotor shaft. This method reduces the cost of the end plate and can secure the end plate firmly to the rotor shaft, but this method will possibly cause thermal deformation of the rotor shaft, which deteriorates the rotational accuracy of the rotor assembly.
Accordingly, it has been desired by the industry to develop a permanent magnet rotor having inexpensive end plates which can secured firmly to the rotor shaft without deteriorating the rotational accuracy of the rotor assembly.


DISCLOSURE OF THE INVENTION

The present invention provides a permanent magnet rotor assembly comprising a rotor shaft, a plurality of yokes arranged around the rotor shaft at circumferential intervals and extending along the axis of the rotor shaft, permanent magnets each being held between the two adjacent yokes, a pair of end plates attached to the opposite ends of the yokes, respectively, each end plate being formed of a non-magnetic material and having in the central portion thereof a boss capable of fitting on the rotor shaft, the boss being secured to the rotor shaft by the compressive force of a fastening ring fitted on the boss by a shrinkage fit.
In the permanent magnet rotor assembly according to the present invention, the boss of the end plate is secured firmly to the rotor shaft by the compressive force of the fastening ring. The fastening ring need not be formed of a nonmagnetic material, and hence the fastening ring is inexpensive. On the other hand, since the end plate formed of a non-magnetic material may have a small thickness, the end plate also is inexpensive. Furthermore, since the end plate can be secured to the rotor shaft without requiring a welding process, thermal deformation of the rotor shaft and deterioration of the rotational accuracy of the rotor assembly can be prevented.
Preferably, the boss of the end plate is formed by drawing. Therefore, the end plate can be easily manufactured at a low cost by using the least possible amount of a non-magnetic material.
The above and other features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a permanent magnet rotor assembly, in a preferred embodiment, according to the p

REFERENCES:
patent: 3908265 (1975-09-01), Heil et al.
patent: 3937993 (1976-02-01), Noodleman
patent: 3979821 (1976-09-01), Noodleman
patent: 4151430 (1979-04-01), Stark

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