JPH03159533A - Super high speed rotor - Google Patents

Abstract

PURPOSE:To enhance tensile strength of a rotor and to protect a magnet against breakdown by fitting a sleeve, for applying compression stress in the axial direction onto a magnet, to the outer circumference of the rotary pole of a rare earth magnet. CONSTITUTION:A permanent magnet 2 comprises a magnetic body containing rare earth elements, and it is magnetized in predetermined direction to provide a rotary pole. A sleeve 3 is shrinkage fitted on the magnet 2 in order to apply a strong compression stress onto the magnet 2 toward the center thereof. Centrifugal force F to be applied on the permanent magnet 2 can be expressed by a formula F=mromega<2>, where (m) is mass, (r) is radius, and omega is rotary angular speed. Predetermined compression stress is previously applied onto the magnet 2 from the outer circumference toward the center through shrinkage fitting of the sleeve 3 so that centrifugal force F during high speed rotation to be applied onto the magnet will be within the allowable limit of tensile force. Since the centrifugal force to be applied onto the rotary pole during high speed rotation does not deviate from the limit of tensile strength of the permanent magnet, the permanent magnet is protected against breakdown.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultra-high-speed rotor of a rotating electrical machine that is directly connected to an ultra-high-speed rotating turbine shaft.

(Prior Art) In recent years, exhaust gas from an internal combustion engine is guided to a turbine, rotated at high speed, and a compressor attached to the turbine shaft is driven.
Turbochargers are widely used to forcefully feed supercharged air to internal combustion engines. A rotating electric machine that serves as an electric generator is attached to the turbine shaft of this type of turbocharger, and the exhaust energy is regenerated as electricity, or power from a battery is supplied to the rotating electric machine to drive it electrically and supercharge it. There are efforts being made to assist the operation. Since the rotor of such a rotating electrical machine placed on the turbine shaft is driven to extremely high speed rotation, it is particularly important to propose a turbocharger generator whose rotor is a permanent magnet that has an outer cylinder to prevent damage caused by centrifugal force. It is disclosed in Kaisho 62-254649. (Problem to be solved by the invention) When the rotational speed of a rotating electric machine is increased, the energy density increases, so it can be made smaller. When permanent magnets are used in the rotor, rare earth magnets with excellent magnetic properties can be used. Will be using it.

However, rare earth magnets, such as rare earth cobalt magnets, have high mechanical strength against compressive stress (approximately 80 kgf/2
), but it has a weak tensile stress of about 5 kgf/III12. Therefore, in the proposal disclosed in the above-mentioned publication, an outer cylinder (sleeve) is provided around the outer circumference of the permanent magnet to prevent destruction, but the centrifugal force (F = mr
It is conceivable that if the tensile stress caused by ω2) exceeds the tensile strength limit of the rare earth magnet, it will break.

The present invention was made in view of such problems,
The purpose is to provide an ultra-high-speed rotor in which the tensile strength of the rotor is increased by applying compressive preload to the permanent magnets of the rotor of a rotating electrical machine that rotates at ultra-high speed.

(Means for Solving the Problems) According to the present invention, a sleeve that applies compressive stress to the permanent magnet in the central axis direction is fitted onto the outer peripheral surface of the rotating magnetic pole of a permanent magnet made of a magnetic material containing rare earth elements. Furthermore, the sleeve is made of a material having a specific elastic modulus three times or more that of the permanent magnet.

(Function) In the present invention, compressive stress is applied toward the center of the rare earth magnet by shrink fitting or a sleeve utilizing the properties of shape memory alloy on the outer periphery of the rotating magnetic pole, so centrifugal force due to high speed rotation is applied. The sleeve has a specific elastic modulus that is more than three times that of a permanent magnet, so it can be used without exceeding the tensile limit of rare earth magnets, especially when the rotation speed exceeds 100,000 rpm. Surface pressure between the sleeves is maintained, thereby preventing destruction of the rare earth magnet due to centrifugal force.

(Example) Next, an example of the present invention will be explained in detail using the drawings. FIG. 1 is a sectional view showing the configuration of a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a rotating shaft made of high-strength steel, which serves as the rotating shaft for, for example, a turbine and a compressor in a turbocharger. It rotates at high speed. 2 is a thick cylindrical rare earth magnet (permanent magnet), made of a magnetic material containing rare earth elements such as samarium-cobalt, and magnetized in a predetermined direction to rotate M18i. An electric motor or generator is created through electromagnetic interaction with the stator. A sleeve 3 is fitted around the outer periphery of the rare earth magnet 2. It is made of strong metal and is fitted by shrink fitting in order to apply a strong compressive stress from the outer peripheral wall of the rare earth magnet 2 toward the center. FIG. 2 is an explanatory diagram of the state immediately before heating the sleeve and shrink-fitting it. The sleeve 3', which has been heated to a predetermined high temperature and has a large diameter, is fitted onto the outer periphery of the rare earth magnet 2. After that, when the sleeve 3゛ is returned to room temperature, the diameter of the sleeve 3゛ becomes smaller, and it is firmly fitted to the outer periphery of the rare earth magnet 2, and further applies compressive stress to the rare earth magnet 2 from the outer peripheral wall toward the center. It is a constricting thing.

Here, as shown in FIG. 1, the centrifugal force F applied to the rare earth magnet 2 is expressed as F=mrω2 when the mass m and the rotation radius r1 are the angular velocity ω.
A predetermined compressive stress is applied to the rare earth magnet 2 from the outer periphery toward the center by shrink fitting, and even if centrifugal force F is applied to the rare earth magnet during high speed rotation, it is configured so that the shrinkage limit is below or below. It is.

In addition, the material of the sleeve 3 is a non-magnetic material with high strength, and the tensile stress of the sleeve itself due to centrifugal force is added to the tensile stress corresponding to the compressive preload applied to the rare earth magnet. The materials used are those that can withstand these stresses. Furthermore, Fig. 3 is a curve diagram showing the relationship between the rotation speed of the rotor and the stress of the sleeve. FIG. 4 is a sectional view of a turbocharger with rotating electric machine to which this embodiment is applied.

Next, referring to the sectional view of FIG. 4, the turbocharger 10 is driven by the exhaust energy of an engine (not shown) to compress air and supply this pressurized air to the engine as supercharging air. 11 is a turbine driven by the exhaust gas from lJt trachea l2; 13 is a compressor connected to turbine 11 by rotary shaft 1 and driven to rotate;
This compresses the air from 4 and sends it to the engine. 15 is a bearing that supports the rotating shaft l;
Rotation between the bearing 15 and the compressor 13 @1
The above-mentioned permanent magnet 2' is attached as a rotating magnetic pole on top. A stator 8 electromagnetically corresponds to the four rotors of the permanent magnet 2, and has a core 81 and a coil 82.

When the exhaust energy from the engine is large and there is surplus power for supercharging the turbocharger 10, the electric power induced in the coil 82 of the stator 8 is used as a power source by changing the magnetic flux caused by the permanent magnet 2 driven at ultra high speed. On the other hand, when the engine is running at low speed and high load with little exhaust energy and sufficient boost pressure cannot be obtained from the turbocharger 10, the TL from the battery is charged.
It is configured to supply fi energy to the stator 8 to move the rotor, energize the supercharging operation of the compressor 13, and increase the boost pressure to the engine. Next, the operation of this embodiment configured as described above will be explained.

When the rotor configured as described above is driven to rotate at extremely high speed by exhaust energy, a strong centrifugal force is applied to the rotor outward from the central axis, causing the permanent magnet 2 and the sleeve 3 to move outward. This will result in a tensile stress of .

As mentioned above, the tensile strength of the rare earth magnet is small at about 5 kgf/■ for the Samarikmu cobalt magnet, but the sleeve 3 fitted around the outer periphery is fitted so as to apply compressive stress to the permanent magnet 2. In this case, the compressive stress of the rare earth magnet is about 80 kgf/Illm2, so
The permanent magnet 2 to which strong compressive stress is applied can withstand centrifugal force during ultra-high speed rotation without deformation or damage.

Next, a second embodiment of the present invention will be described.

FIG. 5 is a sectional view showing the configuration of the second embodiment, in which 1 is a rotating shaft and 2 is a permanent magnet made of a rare earth magnet, which is the same as the vJl diagram. 31 is an outer cylinder made of a shape memory alloy, for example, N i
- A Ti-based alloy is used, which has been subjected to shape memory treatment in advance to a size smaller than the outer diameter of the permanent magnet, and is formed so that the permanent magnet 2 is attached inside at a temperature lower than its transformation temperature. After being attached to the outer periphery of the permanent magnet 2, it is heated to a temperature higher than the transformation temperature of the alloy to firmly fit it. Therefore, after the outer cylinder 31 recovers its shape, it applies compressive stress to the permanent magnet 2 from the outer periphery toward the center, and the ultra-high speed rotation of the rotating magnetic pole is achieved by the operation of the sleeve 3 in the first embodiment described above. Similarly, damage to the permanent magnet 2 made of rare earth magnets is prevented. By the way, even if an interference of 26 is set between the permanent magnet and the sleeve when the rotor is stationary, and compressive preload is applied to the permanent magnet in the direction of the central axis, the surface pressure generally decreases as the rotation increases. descend. The surface pressure Pm between the permanent magnet and the sleeve is ρ 1 ρ2 EI E2 νl ν2 a b C: Permanent magnet density: Sleeve density: Permanent magnet elastic modulus: Sleeve elastic modulus: Permanent magnet Boisson's ratio: Sleeve Boisson's ratio: Inner radius of permanent magnet: Outer radius of sleeve: Outer radius of permanent magnet, (i.e., inner radius of sleeve) ω: Given by angular velocity.

In other words, when the angular velocity of the rotor becomes 100,000 rpm or more,
If the surface pressure Pm between the permanent magnet and the sleeve approaches the above example, the permanent magnet may be destroyed by centrifugal force. especially,
If the specific elastic modulus E2/ρ2 of the sleeve was small, the Pm would drop significantly, and there was a problem that it would not be reinforced at ultra-high speed rotation. Therefore, a third embodiment of the present invention that makes it possible to deal with these problems will be described. FIG. 6 is a sectional view showing the configuration of the third embodiment, and FIG. 7 is a characteristic diagram showing the surface pressure between the sleeve and the permanent magnet. In the figure, a cylindrical permanent magnet 2 is fitted onto a shaft 1, and a sleeve 32 is fitted onto the outer peripheral surface of the permanent magnet 2. 4 is a plate that covers the axial end face of the magnet 2. FIG. 7 shows a state in which the surface pressure Pm between the permanent magnet and the sleeve changes depending on the rotation speed N. Here, in the first term of equation (1) for determining the surface pressure Pm, the upper limit of the interference 2δ at rest is determined by the thermal expansion coefficients of the permanent magnet 2 and the sleeve 32. On the other hand, the second term is proportional to the square of the angular velocity (rotation speed), but its coefficient is generally
positive, and as the angular velocity increases, the reinforcing effect of the sleeve weakens by a little Pmlfn. In the figure, the solid line indicates
A case where the specific elastic modulus E2/ρ2 of the sleeve is small is shown by a dashed-dotted line in comparison with a case where the specific elastic modulus E2/ρ2 of the sleeve is large. This point will be explained below. The angular velocity at the rated rotation is ω. Then, in order to maintain the reinforcing effect of the sleeve 32 even at the rated rotation, if the degree is σ8/ρ2, the stress due to the centrifugal force of the sleeve itself is expressed as follows: Since it is given by VJ, it becomes a condition that the sleeve does not break, so by substituting it into equation (2) above, becomes the necessary condition.

By the way, in an ultra-high speed rotor of 100,000 rpm or more, rare earth magnets with high magnetic energy density are used as permanent magnets in order to downsize the rotor. Since its thermal expansion coefficient is about IOXIO 8, the ratio of interference δ to the inner radius C of the sleeve is δ/ c < 10x loe x 300 = 3
x lj3 is the upper limit. Also, the specific gravity of rare earth magnets is about 8 and the elastic modulus is about 200 GPa, so p l/E, ~ 3'1゜゛'9? ~ 4 ×
1O 2ao z 10'1. However, as the sleeve becomes thicker, the magnetic flux density on the rotor surface decreases and its performance as a magnet decreases.
The limit is about a:c:b~1:3:4. In that case, Boisson's ratio is 0.2 to 0. 3, so set this to 0.2
As. Also, the specific strength σ6/ρ2 of the sleeve material is about 5×10'm at most, so from the above equation (3), -"-
E2 /92 >7. I XIO' ~3 E, /
p. Therefore, in order to maximize the interference δ when stationary, it is necessary to select a material whose specific elastic modulus is three times or more that of a permanent magnet as a sleeve material for an ultra-high-speed rotor that operates at 100,000 rpm or more. For example, silicon nitride, carbon fiber reinforced plastic, and carbon fiber reinforced metal can be pointed out as specific examples of sleeve materials. As described above, according to this embodiment, an ultra-high-speed rotor is constructed of a cylindrical rare earth magnet used as a rotating magnetic pole, a shaft fitted inside the magnet, and a sleeve fitted on the outer peripheral surface of the magnet. In contrast, to the sleeve material,
Using a material with a specific elastic modulus more than three times that of a permanent magnet,
By applying compressive preload, the permanent magnet can be reinforced even at speeds of 100,000 rpm or more, which has the effect of preventing destruction of the permanent magnet.

Although the present invention has been described above using the three embodiments described above, various modifications can be made within the scope of the gist of the present invention, and these modifications are not excluded from the scope of the present invention. (Effects of the Invention) According to the present invention, a sleeve that applies compressive stress in the direction of the central axis is fitted to the outer periphery of a rotating magnetic pole made of a magnet material containing rare earth elements by shrink fitting or by applying the characteristics of a shape memory alloy. As a result, inward compressive stress is always applied to the rare earth magnet, so even if centrifugal force is applied during ultra-high speed rotation of the rotating magnetic poles, the tensile stress limit of the rare earth magnet will not be exceeded. The permanent magnet can be reinforced even at speeds of 100,000 rpm or higher, and its destruction can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the configuration of the first embodiment of the present invention, Fig. 2 is an explanatory diagram of the embodiment immediately before shrink fitting, and Fig. 3 shows the rotation speed of the rotor and the stress of the sleeve. 4 is a sectional view of a turbocharger with a rotating electrical machine to which this embodiment is applied, FIG. 5 is a sectional view showing the configuration of the second embodiment, and FIG. 6 is a sectional view of the FIG. 7 is a sectional view showing the structure of the embodiment of the present invention, and FIG. 7 is a characteristic diagram showing the surface pressure between the sleeve and the permanent magnet. DESCRIPTION OF SYMBOLS 1...Rotating shaft, 2...Permanent magnet, 3...Sleeve (outer cylinder), 10...Turbocharger, 11...Turbine, 13...Compressor.

Claims (4)

[Claims] (1) An ultrahigh-speed rotor characterized in that a sleeve that applies compressive preload in the central axis direction to the permanent magnet is fitted onto the outer peripheral surface of the rotating magnetic pole of a permanent magnet made of a magnetic material containing a rare earth element. (2) Claim (1) characterized in that the sleeve is made of a material having a specific elastic modulus three times or more that of the permanent magnet.
) Ultra high speed rotor. (3) The sleeve is provided with compression preload by shrink fitting or cold fitting.
The ultra-high speed rotor described in 2). (4) The ultra-high speed according to claim (1), wherein the sleeve is made of a shape memory alloy, expanded at a temperature below the transformation temperature of the alloy, attached to a permanent magnet, and fitted by shape recovery. rotor.