GB2166908A - Motor - Google Patents

Abstract

An electric motor having a relatively long shaft 15 includes a journal portion 48 formed over a certain axial length of the rotor surface 22. A plurality of bearing pieces 54 are circumferentially disposed in the inner surface of the stator core 2 at slots 52 in the core for receiving the stator coils 7, the bearing pieces 54 forming an intermediate bearing 49 to bear the journal portion 48 of the rotor during the time it rotates at transitional speed. <IMAGE>

Description

SPECIFICATION Motor The present invention relates to a motor and more particularly to a motor requiring a long rotor such as a submersible motor used for a deep well.

In a submersible motor for use in a deep well, a limitation has been imposed on the length of the rotor relative to the size of the well by the required rigidity of the rotor, particularly of the motor shaft. Accordingly, the length of the rotor has been restricted and, thus, the maximum output of the motor has been limited for respective sizes of wells. This limitation is caused by the fact that the difference between the starting torque and the normal operating torque of the motor is large, the starting torque reaching several to 10 times or more that of the normal operating torque, and to the fact that the unbalanced induction force is greatest on starting.Therefore, the rigidity of the shaft of a long motor may be satisfactory during normal operation but insufficient when starting and during the transition from starting to normal operating speed, if a high power output is required. Therefore, in some instances, such motors are axially coupled to obtain such a high power output.

Also, in a motor having a long shaft, not necessarily limited to a submersible motor for a deep well, an intermediate portion of a motor shaft has been provided with no rotor portion therearound, so as to expose the shaft, which is supported by an intermediate bearing in addition to bearings supporting the opposite end portions of the shaft.

Further, in the case of a canned motor, a bearing portion has been formed on the inner side of the stator can so as to rotatably support a journal portion formed on the outer periphery of the rotor.

However, axial coupling of motors is expensive and results in several drawbacks such as complex construction and wiring, requiring additional sealing means, increased weight, infe rior rigidity at the coupling portion, and insufficient power relative to the lengthwise dimension of the coupled motors.

The idea of supporting the exposed intermediate portion of the shaft is inferior in that the rotor and stator must be separated respectively at their intermediate portions and fabri cation of such divided rotor and stator is une conomical and maintenance or replacement of the intermediate bearing is also impractical.

The proposal above for the canned motor is satisfactory; however, such proposal is not applicable to the non-canned motor to which the present invention is directed. Accordingly, it has been desired to have a non-canned mo tor which is free from the above drawbacks.

It is an object of the present invention to provide a non-canned motor capable of outputting a high power while the ratio of its axial length to its diameter is relatively large.

The above object is accomplished by the present invention as claimed.

An embodiment according to the present invention is constructed to have an intermediate bearing means at the intermediate portion of the relatively long lengthwise dimension wherein a bearing portion of the intermediate bearing means consists of a plurality of bearing pieces each coupled with a wedge member adapted to be inserted in a slot in a stator for holding a stator coil in place and a journal portion of the intermediate bearing means is formed on the intermediate outer peripheral portion of a rotor.

The present invention will further be explained in the following, reference being made to the accompanying drawings, in which: Figure 1 is a longitudinal cross sectional view of a motor according to the present invention; Figure 2 is a cross sectional view, taken normal to the shaft, of a stator core of the motor shown in Fig. 1; Figure 3 is a side view of a combination of a wedge and a bearing piece shown in Fig. 2; Figure 4 is a front view of the combination shown in Fig. 3; Figure 5 is a cross sectional view taken along the line V-V in Fig. 4; Figure 6 is an end view of the combination shown in Figs. 3 and 4; and Figure 7 is a cross sectional view taken along the line VII-VII in Fig. 3.

Referring now to Fig. 1, there is illustrated a longitudinal cross sectional view of a submersible motor suitable for use in a deep well.

Within a cylindrical frame 1 made of sheet metal, a stator 2 is secured and, at the opposite end portions, an upper frame plate 4 and a lower frame plate 5, both being ring shaped, are press fitted and fixed in place. The stator 2 comprises stator coils 7 and the coils 7 are born by a support member 6 preferably made of rubber and disposed between the stator coils 7 and the lower frame plate 5. A coil end insulation paper 8 is disposed on the inner surface of the frame 1 at the portion between the frame 1 and the stator coils 7.

At the upper end of the frame 1, an upper bracket 9 is fitted with a sealing means (not shown) interposed therebetween. A plurality of stud bolts 12 are mounted on the upper frame plate 4, the bolts 12 passing through holes provided with seals in the bracket 9.

Each of the bolts 12 is provided with a hex portion to be engaged by a tool or spanner and adapted for axially mounting a pump. Into the upper bracket 9, an upper radial metal bearing 13 is fitted and held as unrotatable by a pin 14 radially extending into both members.

At the lower part of the frame 1, a lower bracket 18 is fitted with a sealing means (not shown) interposed therebetween and the bracket 18 is secured to the lower frame plate by a plurality of bolts 19. Into the lower bracket 18, a lower radial metal bearing 20 is fitted and held stationary by a radial pin 21 radially extending into both the bracket 18 and the bearing 20.

A motor shaft 15 with a rotor 22 secured thereto is rotatably supported by the upper radial bearing 13 and the lower radial bearing 20, the rotor being positioned with clearance relative to the stator 2. The shaft is also provided with a balancing ring 24 for adjusting the dynamic balance of the rotor assembly consisting of the shaft 15 and the rotor 22.

At the lower end of the frame 1, a thrust housing 31 having the same diameter as that of the frame 1 is coupled to the frame 1 with sealing means (not shown) disposed therebetween and tightened by bolts 32 to the lower frame plate 5, the holes in the bracket 18 for the bolts 32 being sealed by means such as seal washers. The thrust housing 31 attached to the frame 1 forms a thrust bearing chamber 33 and at the bottom of the thrust chamber an adjusting screw 35 is threadably mounted, the top of the adjusting screw 35 being formed in a hemispherical shape. Between the hemispherical top of the screw 35 and the lower and of the motor shaft 15 a thrust bearing assembly 28 is disposed to bear the thrust of the shaft 15.The thrust bearing assembly 28 comprises an upper thrust disk assembly 29 secured to the shaft 15 through a key 25 and a lower thrust pad assembly 36 disposed on the hemispherical top of the bolt 35 so that the opposing surfaces of the upper thrust disk assembly 29 and the lower thrust pad assembly 36 make sliding contact regardless of the tilting of either of the thrust disk assembly or thrust pad assembly.

At the upper portion of the frame 1, a seal 16, a seal cover 42 and a sand-slinger 43 are provided around the shaft 15. Also, a cable 44 connected to the coils 7 is led out from inside the frame 1 through a sealing packing 45 so that the cable 44 may be connected to a power source. In the bracket 9, an inlet port 47 is provided so as to introduce and fill liquid into the motor.

At the central portion on the outer surface of the rotor 22 a journal portion 48 is formed from a suitable material covering a certain axial length of the cylindrical surface so that the diameter of the journal portion 48 becomes somewhat large than that of the rotor 22.

Formation of the journal portion 48 may be effected by such means as metal spraying, hard chromium plating or carbon coating. In the case of metal spraying, molybdenum or TRIBALOY (Trademark of Du Pont) is used.

Alternatively, a thin cylindrical plate of material may be attached in a wrapping manner over the rotor 22 and the ends thereof are welded together. In any case, the journal portion 48 is finished by means such as grinding, lapping or super-finishing. A bearing portion 49 for rotatably supporting the journal portion 48 is formed on the stator side.

In Fig. 2, a cross section of the stator 2 taken normal to the axial direction is shown.

A plurality of axial slots 52 are provided on the inner surface of a stator core 51. Each slot 52 is narrowed at its axial opening 53 and the stator coil 7 is received in the slot 52. A wedge 50 is- inserted into each slot 52 so as to extend over the length of the whole slot to hold the stator coil 7 in place. The wedge 50 is associated with a bearing piece 54 and a combination of the wedge 50 and the bearing piece is illustrated in Figs. 3, 4, 5, 6, and 7.

As shown in these Drawings, the wedge 50 is recessed on one of its surfaces at 59 for a length equal to the bearing piece 54 which is received in the recess 59. The opposite edges of the wedge 50 are straight and thus the transverse cross section of the wedge is a rectangular shape to hold the coil 7 within the slot 52. The bearing piece is fitted in the recess, attached to the recess by bonding, or unitarily formed with the wedge 50. An example of the material to be used for the bearing piece is preferably carbon impregnated fluorine contained polymer or carbon impregnated Nylon; however, other materials may be used.The bearing piece 54 comprises a base 55, a web 56, and a bearing portion 57, the thickness of the base being equal to the depth of the recess 59, the width of the base 55 being equal to that of the wedge 50, and the height of the web 56 being equal to the width of the narrow opening 53. However, in determining the dimensions of the wedge and bearing piece, it should be considered that the insulating paper wrapping the coils will be interposed when the wedge 50 and the bearing piece 54 are inserted. At the side opposite the base 55, the bearing portion 57 is formed to have a width larger than that of the wedge 50 but its width is determined so as not to interfere with the adjacent bearing portion 57 of the adjacent bearing piece. A bearing surface 58 of the bearing portion 57 is formed as a planar surface parallel to the tangential direction of the rotor or a concave surface having a radius of curvature larger than the radius of the journal portion 48.

The clearance in the radial direction between the bearing surface 58 and the journal portion 48 is, just for example, 0.3 mm in a case where the radial clearance between the stator 2 and the rotor 22 is 0.8 - 1 mm. These dimensions are determined so that the shaft 15 may deflect due to the unbalanced inductive force from the magnetic field during the starting period of the motor or during the passing of critical speed after starting, but the deflection is limited to the determined clearance by the intermediate bearing portion 49 and the journal portion 48 may not contact the bearing portion after the shaft speed once passes the critical speed. Naturally no contact is preferred between the bearing portion 49 and the journal portion 48; however, it may not be objectionable if the clearance is arranged so that the journal portion 48 is always born by the bearing surface 58.

Upon actuation of the motor, the motor shaft 15 rotates with its radial load being born by the upper and lower radial bearings 13 and 20 and with its thrust load being born by the thrust bearing assembly 28. Because the starting torque reaches several to 10 times or more that of the rated torque, the rotor 22 rotates with vibration during the transitional period of the speed and the deflection of the journal portion 48 at that time is restricted by the bearing portion 49. Also, in a case where the motor shaft is relatively long and generates flexible vibration at the time of passing the critical speed, the rotor shaft 15 passes the critical speed without problem because the journal portion 48 is supported by the bearing portion during such vibration.

Further, the thrust bearing assembly is arranged to accomodate the radial shifting of the shaft due to flex vibration but the amount of such shifting is made small due to the coaction of the bearing portion 49 and the journal portion 48.

While the location of the journal portion 48 and the bearing portion was described as being central between the upper and lower radial bearings 13 and 20, it may be axially shifted in either an upward or downward direction. If the length of the motor shaft is made very long, the number of bearings and journal portions may be increased, for example, to two at two axial portions. With such arrangement of the intermediate bearing means, the shaft 15 may smoothly pass the critical speed which may cause flexible vibration having nodes.

In the foregoing explanation, the embodiment has been explained as having a bearing piece 54 provided at each of the slots 52; however, a bearing piece does not have to be provided at every slot but they may be disposed at intermittent slots in the circumferential direction. In this case, the wedge 50 is not provided with a recess 59 where a bearing piece is not disposed.

As explained above, the present invention provides a non-canned motor capable of outputting a relatively large power compared to the small size of its radial direction, which is applicable to places where the diameter of the motor is limited. For instance, 45 KW has been the maximum available power for a motor used in a deep well of 8" diameter, but it becomes possible to obtain a power of 75 KW or more for the same diameter according to the present invention. Further, such a motor is inexpensive compared to motors axially coupled to increase power.

Also, the bearing piece may be inserted from the end of the stationary core of the stator, so assembly of the bearing piece will not cause any trouble even if the length of the rotor is long.

While the present invention has been explained in detail referring to the specific embodiment, it is not limited to that explained and it may be modified or changed by those skilled in the art within the spirit and scope of the present invention defined in the Claims annexed hereto. For example, the embodiment was explained as a vertical motor, but it may also be applied to a horizontal motor where the size of the diameter is limited.

Claims (5)

1. A motor comprising: a stator having a cylindrical core provided with a plurality of axial slots on the inner surface which receive stator coils therein; a rotor assembly consisting of a motor shaft and a rotor shaft secured thereto, the shaft being supported at opposite sides of the rotor by radial bearing means so that the rotor is disposed with clearance between the rotor and the stator; a plurality of bearing pices disposed at said slots to form an intermediate bearing between said radial bearing means; and a journal portion formed on the outer surface of said rotor so as to be born against said intermediate bearing upon rotation of the shaft.

2. A motor as claimed in Claim 1 wherein said journal portion is formed by spraying, fusing, or fitting sliding material over the rotor.

3. A motor as claimed in Claim 1 wherein said bearing pieces are disposed so that said journal portion bears against said pieces only during the time when said shaft rotates at transitional speeds of the motor.

4. A motor as claimed in Claim 1 wherein said bearing pieces are intermittently disposed at intermittent slots.

5. A motor substantially as hereinbefore described with reference to the accompanying drawings.