US20060181168A1 - Pump motor with bearing preload - Google Patents
Pump motor with bearing preload Download PDFInfo
- Publication number
- US20060181168A1 US20060181168A1 US10/550,256 US55025605A US2006181168A1 US 20060181168 A1 US20060181168 A1 US 20060181168A1 US 55025605 A US55025605 A US 55025605A US 2006181168 A1 US2006181168 A1 US 2006181168A1
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- US
- United States
- Prior art keywords
- housing
- rotor assembly
- bearing
- assembly
- outer races
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K5/00—Casings; Enclosures; Supports
- H02K5/04—Casings or enclosures characterised by the shape, form or construction thereof
- H02K5/16—Means for supporting bearings, e.g. insulating supports or means for fitting bearings in the bearing-shields
- H02K5/173—Means for supporting bearings, e.g. insulating supports or means for fitting bearings in the bearing-shields using bearings with rolling contact, e.g. ball bearings
- H02K5/1735—Means for supporting bearings, e.g. insulating supports or means for fitting bearings in the bearing-shields using bearings with rolling contact, e.g. ball bearings radially supporting the rotary shaft at only one end of the rotor
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B17/00—Pumps characterised by combination with, or adaptation to, specific driving engines or motors
- F04B17/03—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C25/00—Bearings for exclusively rotary movement adjustable for wear or play
- F16C25/06—Ball or roller bearings
- F16C25/08—Ball or roller bearings self-adjusting
- F16C25/083—Ball or roller bearings self-adjusting with resilient means acting axially on a race ring to preload the bearing
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K5/00—Casings; Enclosures; Supports
- H02K5/04—Casings or enclosures characterised by the shape, form or construction thereof
- H02K5/16—Means for supporting bearings, e.g. insulating supports or means for fitting bearings in the bearing-shields
- H02K5/173—Means for supporting bearings, e.g. insulating supports or means for fitting bearings in the bearing-shields using bearings with rolling contact, e.g. ball bearings
- H02K5/1732—Means for supporting bearings, e.g. insulating supports or means for fitting bearings in the bearing-shields using bearings with rolling contact, e.g. ball bearings radially supporting the rotary shaft at both ends of the rotor
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C19/00—Bearings with rolling contact, for exclusively rotary movement
- F16C19/02—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows
- F16C19/04—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for radial load mainly
- F16C19/06—Bearings with rolling contact, for exclusively rotary movement with bearing balls essentially of the same size in one or more circular rows for radial load mainly with a single row or balls
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49009—Dynamoelectric machine
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49009—Dynamoelectric machine
- Y10T29/49012—Rotor
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49636—Process for making bearing or component thereof
- Y10T29/49643—Rotary bearing
- Y10T29/49679—Anti-friction bearing or component thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49636—Process for making bearing or component thereof
- Y10T29/49698—Demounting
Definitions
- This invention relates generally to electric motors and more particularly to an electric motor intended to be used with a reciprocating load such as a diaphragm pump.
- Electric motors often use bearings to reduce friction, particularly rolling element bearings such as ball bearings.
- Commercially available bearings have some clearance between their individual components, e.g. between the balls and the outer race or the inner race, thereby allowing some degree of radial and axial play.
- the motor is connected to a cyclic load, particularly a radial load (i.e. perpendicular to the motor shaft axis) such as that applied by a diaphragm pump, the interaction of the bearing play with the load may cause the motor life to be appreciably reduced through fatigue, fretting of the motor components, and rapid wear.
- an electrical machine including: a housing assembly having first and second ends; a first bearing mounted in the housing, the first bearing having a plurality of rolling elements disposed between first inner and outer races; and a second bearing mounted in the housing and spaced away from the first bearing, the second bearing having a plurality of rolling elements disposed between second inner and outer races.
- a rotor assembly having first and second ends is mounted in the first and second bearings, respectively, such that the rotor has a predetermined amount of axial and radial play relative to the housing.
- a biasing element is disposed between one of the rotor assembly or the housing and one of the bearings. The biasing element urges the rotor assembly to a preloaded position which eliminates the axial and radial play.
- Each of the first inner and outer races and the second inner and outer races is secured to one of the rotor assembly or to the housing, such that the rotor assembly is retained in the preloaded position.
- first and second outer races are secured to the housing, and the first and second inner races are secured to the shaft.
- the biasing element comprises a spring disposed between the rotor assembly and the first or second inner race.
- the biasing element is a spring disposed between the housing and the first or second outer race.
- the housing assembly includes a generally cylindrical housing including an axially extending portion with a front end plate connected to a front end thereof; and an end bell attached to a rear end of the housing.
- the coefficients of thermal expansion of the housing assembly, the bearings, and the rotor are selected so that the rotor assembly will be retained in the preloaded position over a temperature range of about ⁇ 40° C. to about 105° C.
- the bearings are constructed from high carbon chromium steel and the housing assembly and the rotor assembly are constructed from 400 series stainless steel.
- a method of assembling an electrical machine includes providing a housing having first and second ends; disposing a first bearing in the housing, the first bearing having a plurality of rolling elements disposed between first inner and outer races; disposing a second bearing in the housing, the second bearing having a plurality of rolling elements disposed between second inner and outer races; and providing a rotor assembly having a longitudinally-extending shaft.
- the rotor assembly is rotatably mounted in the housing with the shaft received in the first and second bearings, such that the rotor is in a first position in which it has a predetermined amount of axial and radial play relative to the housing.
- a biasing element is installed between one of the rotor assembly or the housing and one of the bearings, such that the biasing element forces the rotor assembly to a second position in which the axial and radial play is eliminated.
- Each of the first inner and outer races and the second inner and outer races is secured to one of the rotor assembly or to the housing, such that the rotor assembly is retained in the second position.
- first and second outer races are secured to the housing, and the first and second inner races are secured to the shaft
- the biasing element comprises a spring disposed between the housing and the first or second outer race.
- each of the first inner and outer races and the second inner and outer races is secured by a method selected from the group consisting of: press fitting, adhesive bonding, welding, or brazing
- an electric motor includes a generally cylindrical housing assembly having first and second ends, the housing defining first and second spaced-apart bearing pockets; a first bearing having a plurality of rolling elements disposed between first inner and outer races, the first outer race being received in the first bearing pocket; a second bearing having a plurality of rolling elements disposed between second inner and outer races, the second outer race being received in the second bearing pocket; and a rotor assembly including a shaft received in the first and second inner races, such that the rotor has a predetermined amount of axial and radial play relative to the housing.
- a biasing element is disposed between one of the rotor assembly or the housing and one of the bearings which urges the rotor assembly to a preloaded position which eliminates the axial and radial play.
- the first inner and outer races are secured to the shaft, and the second inner and outer races are secured to the housing, such that the rotor assembly is retained in the preloaded position.
- FIG. 1 is a side elevational view of a ball bearing in a rest condition.
- FIG. 2 is a side elevational view of the ball bearing of FIG. 1 in a preloaded condition.
- FIG. 3 is enlarged view of a portion of the bearing of FIG. 2 .
- FIG. 5 is a side elevational view of a first alternative arrangement of the components of the motor of FIG. 4 .
- FIG. 6 is a side elevational view of a second alternative arrangement of the components of the motor of FIG. 4 .
- FIG. 7 is a side elevational view of a third alternative arrangement of the components of the motor of FIG. 4 .
- FIG. 8 is a side elevational view of a second embodiment of a motor constructed in accordance with the present invention.
- FIG. 9 is a side elevational view of a first alternative arrangement of the components of the motor of FIG. 8 .
- FIG. 10 is a side elevational view of a second alternative arrangement of the components of the motor of FIG. 8 .
- FIG. 11 is a side elevational view of a third alternative arrangement of the components of the motor of FIG. 8 .
- FIG. 1 shows a schematic view of a typical ball bearing 1 including generally cylindrical, concentrically disposed inner and outer races 2 and 3 .
- An array of balls 4 are mounted between the races.
- the balls 4 may be separated and located by a cage 5 as shown.
- the balls 4 are received in arcuate grooves 6 and 7 formed in the inner and outer races respectively.
- the grooves have a radius of curvature greater than the radius of the balls 4 , so that when assembled the balls 4 will have a point contact with the races.
- the bearing 1 Because of spacing between the various elements, the bearing 1 has a radial clearance in the direction denoted “R”, and an axial clearance in the direction denoted “A”. These clearances allow relative radial and axial motion between the inner race 2 and the outer race 3 .
- FIG. 2 depicts the bearing 1 in a preloaded condition.
- An axial preload force is applied to the bearing 1 in the direction of arrow P. This causes the inner race 2 to shift axially with respect to the outer race 3 .
- the axial motion is stopped by the interference of the balls 4 with the grooves in the inner and outer races 2 and 3 .
- relative axial motion of the bearing races causes a wedging effect which prevents relative radial motion between the inner and outer races.
- an axial preload may be used to remove both axial and radial play from a ball bearing.
- FIG. 4 shows a first embodiment of a motor 10 constructed in accordance with the present invention.
- the illustrated example is of a brushless permanent magnet DC motor, but the operative principle of the present invention is equally application to other types of motors as well.
- the basic components of the motor 10 are a housing 12 , an end bell 14 , a stator 16 , a rotor assembly 18 , a front bearing 20 , a rear bearing 22 , and a spring 24 .
- the housing 12 is a generally cylindrical, open-ended member including an axially extending portion 26 and a front end plate 28 which has a front bearing pocket 30 formed therein.
- the front end plate portion of the housing 12 could also be a separate component attached by a variety of methods, for example, screws, press fit, welding, etc.
- the housing 12 may be formed by any known method including casting, forging, machining, powder metallurgy, etc.
- the end bell 14 is a member adapted to close off the rear end of the housing 12 and is attached to the rear end of the housing 12 , for example by the machine screws 32 shown in FIG. 4 .
- the end bell 14 has a rear bearing pocket 34 formed therein.
- the stator 16 is of a known type comprising an array of flat plates wound with coils of wire.
- the rotor assembly 18 comprises a shaft 36 having a central portion 38 , an axially extending front shaft extension 40 , and an axially extending rear shaft extension 42 .
- a plurality of permanent magnets 44 are secured to the outer surface of the central portion, for example with an adhesive.
- the front bearing 20 is of a known rolling-element type such as a ball bearing. Its outer race 46 is received in the front bearing pocket 30 , and its inner race 48 receives the front shaft extension 40 of the rotor assembly 18 .
- the rear bearing 22 is also of a known rolling-element type such as a ball bearing. Its outer race 50 is received in the rear bearing pocket 34 , and its inner race 52 receives a portion of the rear shaft extension 42 .
- the spring is a compression-type coil spring.
- the spring 24 may be of any type which fits in the space provided for it and which provides the required preload force.
- a Belleville spring washer could be used, for example.
- the motor 10 is assembled so that a preload is applied to the bearings 20 and 22 which removes all axial and radial play in each bearing as described above.
- the preload is applied such that the inner races of the bearings are axially biased in opposite directions.
- An exemplary assembly sequence is as follows.
- the rear bearing 22 is assembled to the end bell 14 .
- the outer race 50 of the rear bearing 22 is secured to the end bell 14 so that it cannot move relative to the end bell 14 , for example by press fit, adhesive, tack welding, brazing, or the like.
- the front bearing 20 is then assembled to the housing 12 .
- the outer race 46 of the front bearing 20 is secured to the housing 12 so that it cannot move relative to the housing 12 , in a manner similar to the rear bearing 22 .
- the spring 24 is then assembled to the front shaft extension 40 of the rotor assembly 18 , and the rotor assembly 18 is then inserted in the housing 12 .
- One end of the spring 24 bears against the inner race 48 of the front bearing 20 and the other end of the spring 24 bears against the central portion 38 of the rotor assembly 18 .
- the end bell 14 is subsequently attached to the housing 12 which places the rear shaft extension 42 into the inner race 52 of the rear bearing 22 .
- the action of the compressed spring 24 forces the inner races of each bearing outward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of the spring 24 .
- the inner race 48 of the front bearing 20 is secured to the front shaft extension 40
- the inner race 52 of the rear bearing 22 is secured to rear shaft extension 42 , so that no relative motion can take place between either of the inner races and the rotor assembly 18 .
- the inner races may be secured to the rotor assembly 18 by a variety of methods, as described above.
- the components of the motor 10 are secured in a position which maintains the preload created by the spring 24 during the assembly process.
- the arrangement eliminates all axial and radial play from the bearings and shaft.
- FIG. 5 illustrates a motor 110 which is a variation of the motor 10 depicted in FIG. 4 .
- the spring 24 is placed over the rear shaft extension 42 of the rotor assembly 18 , between the central portion 38 of the shaft 36 and the inner race 52 of the rear bearing 22 .
- the assembly and operation of the motor 110 is otherwise similar to that of the example illustrated in FIG. 4 and described above.
- FIG. 6 illustrates another variation 210 of the motor 10 .
- the construction is again generally similar to that illustrated in FIG. 4 above, the primary difference being that the spring 24 bears on the outer race of the bearings, as described in detail below.
- Assembly of the motor 210 starts with the front bearing 20 being assembled to the housing 12 .
- the outer race 46 of the front bearing 20 is secured to the housing 12 so that it cannot move relative to the housing 12 , for example by press fit, adhesive, tack welding, brazing, or the like.
- the rotor assembly 18 is assembled to the housing 12 .
- the inner race 48 of the front bearing 20 is secured to the front shaft extension 40 so that it cannot move relative to the front shaft extension 40 .
- the rear bearing 22 is then assembled to the rotor assembly 18 .
- the inner race 52 of the rear bearing 22 is secured to the rear shaft extension so it cannot move relative to the rear shaft extension.
- the spring 24 is assembled to the end bell 14 , being inserted in the rear bearing pocket.
- the end bell 14 is then assembled to the housing 12 which inserts the rear bearing 22 into the end bell 14 .
- the spring 24 thus mates between the end bell 14 and the outer race 50 of the rear bearing 22 .
- the action of the compressed spring 24 forces the inner races of each bearing outward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of the spring 24 .
- the outer race 50 of the rear bearing 22 is secured to the end bell 14 , so that no relative motion can take place between the outer race 50 and the end bell 14 .
- the outer race 50 may be secured to the end bell 14 by a variety of methods, as described above.
- the components of the motor 210 are secured in a position which maintains the preload provided by the spring 24 during the assembly process. This arrangement eliminates all axial and radial play from the bearing/shaft mechanism.
- FIG. 7 illustrates a variation 310 of the motor 210 .
- the spring 24 is placed over the front shaft extension 40 of the rotor assembly 18 , between the housing 12 and the outer race 50 of the rear bearing 22 .
- the assembly and operation of this variation is otherwise similar to that of the example illustrated in FIG. 6 and described above.
- FIG. 8 shows a second embodiment of a motor 410 constructed in accordance with the present invention.
- This type of motor is sometimes referred to as a cantilevered design because of the relationship of the rotor assembly to the bearings. Elements in common with the motors depicted in FIGS. 4-7 are shown in prime reference numerals.
- the basic components of the motor 410 are a housing 12 ′, a stator 16 ′, a rotor assembly 18 ′, a front bearing 20 ′, a rear bearing 22 ′, and a preload spring 24 ′.
- the housing 12 ′ is a generally cylindrical, open-ended member including outer axially extending portion 26 ′, an inner axially extending portion 27 , and a front end plate 28 ′.
- the inner axially extending portion 27 defines a front bearing pocket 30 ′ and a rear bearing pocket 34 ′.
- the housing 12 ′ may be formed by any known method including casting, forging, machining, powder metallurgy, etc.
- the stator 16 ′ is of a known type comprising an array of flat plates wound with coils of wire.
- the rotor assembly 18 ′ comprises a shaft 36 ′, a magnet hub 37 attached to the rear end of the shaft 36 ′, and a plurality of permanent magnets 44 ′ secured to the outer surface of the magnet hub 37 , for example with an adhesive.
- the front bearing 20 ′ is of a known rolling-element type such as a ball bearing.
- the spring is a compression-type coil spring.
- the spring 24 ′ may be of any type which fits in the space provided for it and which provides the required preload force.
- a Belleville spring washer could be used, for example.
- the motor 410 is assembled so that a preload is applied to the bearings 20 ′ and 22 ′ which removes all axial and radial play in each bearing as described above.
- the preload is applied such that the bearings are axially biased in opposite directions.
- An exemplary assembly sequence is as follows. First, the spring 24 ′ is assembled to the rotor assembly 18 ′.
- the rear bearing 22 ′ is assembled to the housing 12 ′.
- the outer race 50 ′ of the rear bearing 22 ′ is secured to the housing 12 ′ so that no relative motion can take place between the outer race 50 ′ and the housing 12 ′, for example by press fit, tack welding, brazing, adhesive, etc.
- the front bearing 20 ′ is assembled to the housing 12 ′.
- the outer race 46 ′ of the front bearing 20 ′ is secured to the housing 12 ′ so that no relative motion can take place between the outer race 46 ′ and the housing 12 ′.
- the rotor assembly 18 ′ is assembled to the housing 12 ′, placing the shaft 36 ′ into the inner races of each bearing.
- a lock ring 54 is then assembled to the front end of the shaft 36 ′. This compresses the spring 24 ′.
- the action of the compressed spring 24 ′ forces the inner races of each bearing inward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of the spring 24 ′.
- FIG. 9 illustrates a motor 510 which is a variation of the motor 410 depicted in FIG. 8 .
- the spring 24 ′ is placed over the front end of the shaft 36 ′ between the lock ring 54 and the inner race 48 ′ of the front bearing 20 ′.
- the assembly and operation of the motor 510 is otherwise similar to that of the example illustrated in FIG. 8 and described above.
- FIG. 10 illustrates another variation 610 of the motor 410
- the construction is again generally similar to that illustrated in FIG. 8 above, the primary difference being that the spring 24 ′ bears on the outer race of the bearings, as described in detail below.
- the spring 24 ′ is assembled to the housing 12 ′.
- the rear bearing 22 ′ is then assembled to the rotor assembly 18 ′.
- the inner race 52 ′ of the rear bearing 22 ′ is secured to the shaft so that no relative motion can take place between the inner race 52 ′ and the shaft 36 ′, for example by press fit, tack welding, brazing, adhesive, etc.
- the front bearing 20 ′ is assembled to the housing 12 ′.
- the outer race 46 ′ of the front bearing is secured to the housing 12 ′ so that no relative motion can take place between the outer race 46 ′ and the housing 12 ′, in a manner described above.
- the rotor assembly 18 ′ is assembled to the housing 12 ′. This places the shaft 36 ′ into the inner race 48 ′ of the front bearing 20 ′. A lock ring 54 is then assembled to the shaft 36 ′. This compresses the spring 24 ′. The action of the compressed spring 24 ′ forces the inner races of each bearing inward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of the spring 24 ′.
- FIG. 11 illustrates a motor 710 which is a variation of the motor 610 depicted in FIG. 10 .
- the spring 24 ′ is placed over the front end of the shaft 36 ′ between end of the front bearing pocket 30 ′ and the outer race 46 ′ of the front bearing 20 ′.
- the assembly and operation of the motor 710 is otherwise similar to that of the example illustrated in FIG. 10 and described above.
- a preload be applied to remove axial and radial play from the rotor and bearing assemblies, and that the inner and outer race of each of the bearings be secured such that no relative motion can take place between the race and the mating component.
- a preload must be maintained over the motor's operating temperature range adequate to preserve a zero-play condition in the axial and radial directions, under the expected loads. This is accomplished by the selection of materials used for the housing, rotor assembly, and bearings based on their coefficients of thermal expansion. The difference in coefficients of thermal expansion of the various components is minimized.
- the absolute value of the coefficient of linear thermal expansion of each component is minimized, because even if all of the components are of the same material, excessive thermal expansion will cause loss of the bearing preload if the coefficient of linear thermal expansion is too high.
- materials which are known to exceed the required coefficient of linear thermal expansion include brass, zinc, and aluminum.
- the bearings may be made of a stainless steel alloy such as high carbon chromium steel, JIS G4805/SUJ2. This is consistent with the alloys used in commercially available ball bearings, and provides a baseline for the coefficient of linear thermal expansion to be matched by the other motor components. Accordingly, the housing, shaft and end bell may be made from a stainless steel alloy, such as a 400-series alloy. Alternatively, some of these parts could be made from a low-carbon steel. This combination of materials will preserve an adequate preload over the operating temperature of a typical motor, for example from about ⁇ 40° C. ( ⁇ 40° F.) to about 105° C. (220° F.).
Abstract
Description
- This invention relates generally to electric motors and more particularly to an electric motor intended to be used with a reciprocating load such as a diaphragm pump. Electric motors often use bearings to reduce friction, particularly rolling element bearings such as ball bearings. Commercially available bearings have some clearance between their individual components, e.g. between the balls and the outer race or the inner race, thereby allowing some degree of radial and axial play. In an application where the motor is connected to a cyclic load, particularly a radial load (i.e. perpendicular to the motor shaft axis) such as that applied by a diaphragm pump, the interaction of the bearing play with the load may cause the motor life to be appreciably reduced through fatigue, fretting of the motor components, and rapid wear.
- Attempts have been made to apply a preload to motor bearing assemblies to remove play. However, in operation the motor will be subject to changing internal temperatures, resulting from heat generated by the motor itself or absorbed from the environment in which the motor operates. The parts of the motor responsible for creating the bearing preload condition have differing rates of thermal expansion. This varying thermal expansion may cause the preload on the bearings to be lost, resulting in the accelerated wear described above. The varying thermal expansion may also cause an excessive axial and/or radial load to be placed on the bearings thus also accelerating wear.
- Accordingly, it is an object of the invention to provide a motor in which the radial and axial play is eliminated from the bearings thereof.
- it is another object of the invention to provide a motor having a consistent preload under all operating conditions.
- It is another object of the invention to provide a method of assembling a motor which eliminates radial and axial play from the bearings.
- These and other objects of the present invention are achieved in the preferred embodiments disclosed below by providing. an electrical machine, including: a housing assembly having first and second ends; a first bearing mounted in the housing, the first bearing having a plurality of rolling elements disposed between first inner and outer races; and a second bearing mounted in the housing and spaced away from the first bearing, the second bearing having a plurality of rolling elements disposed between second inner and outer races.
- A rotor assembly having first and second ends is mounted in the first and second bearings, respectively, such that the rotor has a predetermined amount of axial and radial play relative to the housing. A biasing element is disposed between one of the rotor assembly or the housing and one of the bearings. The biasing element urges the rotor assembly to a preloaded position which eliminates the axial and radial play. Each of the first inner and outer races and the second inner and outer races is secured to one of the rotor assembly or to the housing, such that the rotor assembly is retained in the preloaded position.
- According to another embodiment of the invention, the first and second outer races are secured to the housing, and the first and second inner races are secured to the shaft.
- According to another embodiment of the invention, the biasing element comprises a spring disposed between the rotor assembly and the first or second inner race.
- According to another embodiment of the invention, the biasing element is a spring disposed between the housing and the first or second outer race.
- According to another embodiment of the invention, the housing assembly includes a generally cylindrical housing including an axially extending portion with a front end plate connected to a front end thereof; and an end bell attached to a rear end of the housing.
- According to another embodiment of the invention, the coefficients of thermal expansion of the housing assembly, the bearings, and the rotor are selected so that the rotor assembly will be retained in the preloaded position over a temperature range of about −40° C. to about 105° C.
- According to another embodiment of the invention, the bearings are constructed from high carbon chromium steel and the housing assembly and the rotor assembly are constructed from 400 series stainless steel.
- According to another embodiment of the invention, a method of assembling an electrical machine includes providing a housing having first and second ends; disposing a first bearing in the housing, the first bearing having a plurality of rolling elements disposed between first inner and outer races; disposing a second bearing in the housing, the second bearing having a plurality of rolling elements disposed between second inner and outer races; and providing a rotor assembly having a longitudinally-extending shaft.
- The rotor assembly is rotatably mounted in the housing with the shaft received in the first and second bearings, such that the rotor is in a first position in which it has a predetermined amount of axial and radial play relative to the housing. A biasing element is installed between one of the rotor assembly or the housing and one of the bearings, such that the biasing element forces the rotor assembly to a second position in which the axial and radial play is eliminated. Each of the first inner and outer races and the second inner and outer races is secured to one of the rotor assembly or to the housing, such that the rotor assembly is retained in the second position.
- According to another embodiment of the invention, the first and second outer races are secured to the housing, and the first and second inner races are secured to the shaft
- According to another embodiment of the invention, the biasing element comprises a spring disposed between the housing and the first or second outer race.
- According to another embodiment of the invention, each of the first inner and outer races and the second inner and outer races is secured by a method selected from the group consisting of: press fitting, adhesive bonding, welding, or brazing
- According to another embodiment of the invention, an electric motor, includes a generally cylindrical housing assembly having first and second ends, the housing defining first and second spaced-apart bearing pockets; a first bearing having a plurality of rolling elements disposed between first inner and outer races, the first outer race being received in the first bearing pocket; a second bearing having a plurality of rolling elements disposed between second inner and outer races, the second outer race being received in the second bearing pocket; and a rotor assembly including a shaft received in the first and second inner races, such that the rotor has a predetermined amount of axial and radial play relative to the housing.
- A biasing element is disposed between one of the rotor assembly or the housing and one of the bearings which urges the rotor assembly to a preloaded position which eliminates the axial and radial play. The first inner and outer races are secured to the shaft, and the second inner and outer races are secured to the housing, such that the rotor assembly is retained in the preloaded position.
- The subject matter that is regarded as the invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
-
FIG. 1 is a side elevational view of a ball bearing in a rest condition. -
FIG. 2 is a side elevational view of the ball bearing ofFIG. 1 in a preloaded condition. -
FIG. 3 is enlarged view of a portion of the bearing ofFIG. 2 . -
FIG. 4 is a side elevational view of a first embodiment of a motor constructed in accordance with the present invention. -
FIG. 5 is a side elevational view of a first alternative arrangement of the components of the motor ofFIG. 4 . -
FIG. 6 is a side elevational view of a second alternative arrangement of the components of the motor ofFIG. 4 . -
FIG. 7 is a side elevational view of a third alternative arrangement of the components of the motor ofFIG. 4 . -
FIG. 8 is a side elevational view of a second embodiment of a motor constructed in accordance with the present invention. -
FIG. 9 is a side elevational view of a first alternative arrangement of the components of the motor ofFIG. 8 . -
FIG. 10 is a side elevational view of a second alternative arrangement of the components of the motor ofFIG. 8 . -
FIG. 11 is a side elevational view of a third alternative arrangement of the components of the motor ofFIG. 8 . - Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
FIG. 1 shows a schematic view of a typical ball bearing 1 including generally cylindrical, concentrically disposed inner andouter races balls 4 are mounted between the races. Theballs 4 may be separated and located by acage 5 as shown. Theballs 4 are received inarcuate grooves balls 4, so that when assembled theballs 4 will have a point contact with the races. Because of spacing between the various elements, the bearing 1 has a radial clearance in the direction denoted “R”, and an axial clearance in the direction denoted “A”. These clearances allow relative radial and axial motion between theinner race 2 and theouter race 3. -
FIG. 2 depicts the bearing 1 in a preloaded condition. An axial preload force is applied to the bearing 1 in the direction of arrow P. This causes theinner race 2 to shift axially with respect to theouter race 3. As shown more clearly inFIG. 3 , The axial motion is stopped by the interference of theballs 4 with the grooves in the inner andouter races - Turning now to the present invention,
FIG. 4 shows a first embodiment of amotor 10 constructed in accordance with the present invention. The illustrated example is of a brushless permanent magnet DC motor, but the operative principle of the present invention is equally application to other types of motors as well. The basic components of themotor 10 are ahousing 12, anend bell 14, astator 16, arotor assembly 18, afront bearing 20, arear bearing 22, and aspring 24. Thehousing 12 is a generally cylindrical, open-ended member including anaxially extending portion 26 and afront end plate 28 which has afront bearing pocket 30 formed therein. The front end plate portion of thehousing 12 could also be a separate component attached by a variety of methods, for example, screws, press fit, welding, etc. Thehousing 12 may be formed by any known method including casting, forging, machining, powder metallurgy, etc. Theend bell 14 is a member adapted to close off the rear end of thehousing 12 and is attached to the rear end of thehousing 12, for example by themachine screws 32 shown inFIG. 4 . Theend bell 14 has arear bearing pocket 34 formed therein. Thestator 16 is of a known type comprising an array of flat plates wound with coils of wire. Therotor assembly 18 comprises ashaft 36 having acentral portion 38, an axially extendingfront shaft extension 40, and an axially extendingrear shaft extension 42. A plurality ofpermanent magnets 44 are secured to the outer surface of the central portion, for example with an adhesive. Thefront bearing 20 is of a known rolling-element type such as a ball bearing. Itsouter race 46 is received in thefront bearing pocket 30, and itsinner race 48 receives thefront shaft extension 40 of therotor assembly 18. Therear bearing 22 is also of a known rolling-element type such as a ball bearing. Itsouter race 50 is received in therear bearing pocket 34, and itsinner race 52 receives a portion of therear shaft extension 42. In the illustrated example the spring is a compression-type coil spring. However, thespring 24 may be of any type which fits in the space provided for it and which provides the required preload force. A Belleville spring washer could be used, for example. - The
motor 10 is assembled so that a preload is applied to thebearings rear bearing 22 is assembled to theend bell 14. Theouter race 50 of therear bearing 22 is secured to theend bell 14 so that it cannot move relative to theend bell 14, for example by press fit, adhesive, tack welding, brazing, or the like. Thefront bearing 20 is then assembled to thehousing 12. Theouter race 46 of thefront bearing 20 is secured to thehousing 12 so that it cannot move relative to thehousing 12, in a manner similar to therear bearing 22. - The
spring 24 is then assembled to thefront shaft extension 40 of therotor assembly 18, and therotor assembly 18 is then inserted in thehousing 12. One end of thespring 24 bears against theinner race 48 of thefront bearing 20 and the other end of thespring 24 bears against thecentral portion 38 of therotor assembly 18. Theend bell 14 is subsequently attached to thehousing 12 which places therear shaft extension 42 into theinner race 52 of therear bearing 22. The action of thecompressed spring 24 forces the inner races of each bearing outward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of thespring 24. - Finally, the
inner race 48 of thefront bearing 20 is secured to thefront shaft extension 40, and theinner race 52 of therear bearing 22 is secured torear shaft extension 42, so that no relative motion can take place between either of the inner races and therotor assembly 18. The inner races may be secured to therotor assembly 18 by a variety of methods, as described above. Thus, the components of themotor 10 are secured in a position which maintains the preload created by thespring 24 during the assembly process. The arrangement eliminates all axial and radial play from the bearings and shaft. -
FIG. 5 illustrates amotor 110 which is a variation of themotor 10 depicted inFIG. 4 . In this instance, thespring 24 is placed over therear shaft extension 42 of therotor assembly 18, between thecentral portion 38 of theshaft 36 and theinner race 52 of therear bearing 22. The assembly and operation of themotor 110 is otherwise similar to that of the example illustrated inFIG. 4 and described above. -
FIG. 6 illustrates anothervariation 210 of themotor 10. The construction is again generally similar to that illustrated inFIG. 4 above, the primary difference being that thespring 24 bears on the outer race of the bearings, as described in detail below. - Assembly of the
motor 210 starts with thefront bearing 20 being assembled to thehousing 12. Theouter race 46 of thefront bearing 20 is secured to thehousing 12 so that it cannot move relative to thehousing 12, for example by press fit, adhesive, tack welding, brazing, or the like. Therotor assembly 18 is assembled to thehousing 12. Theinner race 48 of thefront bearing 20 is secured to thefront shaft extension 40 so that it cannot move relative to thefront shaft extension 40. - The
rear bearing 22 is then assembled to therotor assembly 18. Theinner race 52 of therear bearing 22 is secured to the rear shaft extension so it cannot move relative to the rear shaft extension. Thespring 24 is assembled to theend bell 14, being inserted in the rear bearing pocket. Theend bell 14 is then assembled to thehousing 12 which inserts therear bearing 22 into theend bell 14. Thespring 24 thus mates between theend bell 14 and theouter race 50 of therear bearing 22. - The action of the
compressed spring 24 forces the inner races of each bearing outward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of thespring 24. - Finally, the
outer race 50 of therear bearing 22 is secured to theend bell 14, so that no relative motion can take place between theouter race 50 and theend bell 14. Theouter race 50 may be secured to theend bell 14 by a variety of methods, as described above. Thus, the components of themotor 210 are secured in a position which maintains the preload provided by thespring 24 during the assembly process. This arrangement eliminates all axial and radial play from the bearing/shaft mechanism. -
FIG. 7 illustrates avariation 310 of themotor 210. In this instance, thespring 24 is placed over thefront shaft extension 40 of therotor assembly 18, between thehousing 12 and theouter race 50 of therear bearing 22. The assembly and operation of this variation is otherwise similar to that of the example illustrated inFIG. 6 and described above. -
FIG. 8 shows a second embodiment of amotor 410 constructed in accordance with the present invention. This type of motor is sometimes referred to as a cantilevered design because of the relationship of the rotor assembly to the bearings. Elements in common with the motors depicted inFIGS. 4-7 are shown in prime reference numerals. The basic components of themotor 410 are ahousing 12′, astator 16′, arotor assembly 18′, afront bearing 20′, arear bearing 22′, and apreload spring 24′. Thehousing 12′ is a generally cylindrical, open-ended member including outer axially extendingportion 26′, an inneraxially extending portion 27, and afront end plate 28′. The inner axially extendingportion 27 defines afront bearing pocket 30′ and arear bearing pocket 34′. Thehousing 12′ may be formed by any known method including casting, forging, machining, powder metallurgy, etc. Thestator 16′ is of a known type comprising an array of flat plates wound with coils of wire. Therotor assembly 18′ comprises ashaft 36′, amagnet hub 37 attached to the rear end of theshaft 36′, and a plurality ofpermanent magnets 44′ secured to the outer surface of themagnet hub 37, for example with an adhesive. Thefront bearing 20′ is of a known rolling-element type such as a ball bearing. Itsouter race 46′ is received in thefront bearing pocket 30′, and itsinner race 48′ receives thefront shaft extension 40′ of therotor assembly 18′. Therear bearing 22′ is also of a known rolling-element type such as a ball bearing. Itsouter race 50′ is received in therear bearing pocket 34′, and itsinner race 52′ receives a portion of theshaft 36′. In the illustrated example the spring is a compression-type coil spring. However, thespring 24′ may be of any type which fits in the space provided for it and which provides the required preload force. A Belleville spring washer could be used, for example. - The
motor 410 is assembled so that a preload is applied to thebearings 20′ and 22′ which removes all axial and radial play in each bearing as described above. The preload is applied such that the bearings are axially biased in opposite directions. An exemplary assembly sequence is as follows. First, thespring 24′ is assembled to therotor assembly 18′. Therear bearing 22′ is assembled to thehousing 12′. Theouter race 50′ of therear bearing 22′ is secured to thehousing 12′ so that no relative motion can take place between theouter race 50′ and thehousing 12′, for example by press fit, tack welding, brazing, adhesive, etc. - The
front bearing 20′ is assembled to thehousing 12′. Theouter race 46′ of thefront bearing 20′ is secured to thehousing 12′ so that no relative motion can take place between theouter race 46′ and thehousing 12′. - Next, the
rotor assembly 18′ is assembled to thehousing 12′, placing theshaft 36′ into the inner races of each bearing. Alock ring 54 is then assembled to the front end of theshaft 36′. This compresses thespring 24′. The action of thecompressed spring 24′ forces the inner races of each bearing inward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of thespring 24′. - Finally, the inner races of both the
front bearing 20′ and the rear bearing are secured to theshaft 36′ so that no relative motion can take place between the inner races and theshaft 36′, in a manner described above. This arrangement eliminates all axial and radial play from the bearing and shaft mechanism. -
FIG. 9 illustrates amotor 510 which is a variation of themotor 410 depicted inFIG. 8 . In this instance, thespring 24′ is placed over the front end of theshaft 36′ between thelock ring 54 and theinner race 48′ of thefront bearing 20′. The assembly and operation of themotor 510 is otherwise similar to that of the example illustrated inFIG. 8 and described above. -
FIG. 10 illustrates anothervariation 610 of themotor 410 The construction is again generally similar to that illustrated inFIG. 8 above, the primary difference being that thespring 24′ bears on the outer race of the bearings, as described in detail below. - First, the
spring 24′ is assembled to thehousing 12′. Therear bearing 22′ is then assembled to therotor assembly 18′. Theinner race 52′ of therear bearing 22′ is secured to the shaft so that no relative motion can take place between theinner race 52′ and theshaft 36′, for example by press fit, tack welding, brazing, adhesive, etc. - The
front bearing 20′ is assembled to thehousing 12′. Theouter race 46′ of the front bearing is secured to thehousing 12′ so that no relative motion can take place between theouter race 46′ and thehousing 12′, in a manner described above. - The
rotor assembly 18′ is assembled to thehousing 12′. This places theshaft 36′ into theinner race 48′ of thefront bearing 20′. Alock ring 54 is then assembled to theshaft 36′. This compresses thespring 24′. The action of thecompressed spring 24′ forces the inner races of each bearing inward into a condition where all axial and radial play is eliminated. This creates a preload force of a magnitude determined by the characteristics of thespring 24′. - Finally, the inner race of the
front bearing 20′ is secured to theshaft 36 and theouter race 50′ of therear bearing 22′ is secured to thehousing 12′ so that no relative motion can take place between these components, in a manner described above. This arrangement eliminates all axial and radial play from the bearing and shaft mechanism. -
FIG. 11 illustrates amotor 710 which is a variation of themotor 610 depicted inFIG. 10 . In this instance, thespring 24′ is placed over the front end of theshaft 36′ between end of thefront bearing pocket 30′ and theouter race 46′ of thefront bearing 20′. The assembly and operation of themotor 710 is otherwise similar to that of the example illustrated inFIG. 10 and described above. - While several basic configurations and methods of assembly have been described above, it is noted that the specific configuration or assembly sequence is not critical to the present invention. Rather, it is important that a preload be applied to remove axial and radial play from the rotor and bearing assemblies, and that the inner and outer race of each of the bearings be secured such that no relative motion can take place between the race and the mating component. Furthermore, a preload must be maintained over the motor's operating temperature range adequate to preserve a zero-play condition in the axial and radial directions, under the expected loads. This is accomplished by the selection of materials used for the housing, rotor assembly, and bearings based on their coefficients of thermal expansion. The difference in coefficients of thermal expansion of the various components is minimized. Furthermore, the absolute value of the coefficient of linear thermal expansion of each component is minimized, because even if all of the components are of the same material, excessive thermal expansion will cause loss of the bearing preload if the coefficient of linear thermal expansion is too high. Examples of materials which are known to exceed the required coefficient of linear thermal expansion include brass, zinc, and aluminum.
- An example of a suitable combination of materials is as follows. The bearings may be made of a stainless steel alloy such as high carbon chromium steel, JIS G4805/SUJ2. This is consistent with the alloys used in commercially available ball bearings, and provides a baseline for the coefficient of linear thermal expansion to be matched by the other motor components. Accordingly, the housing, shaft and end bell may be made from a stainless steel alloy, such as a 400-series alloy. Alternatively, some of these parts could be made from a low-carbon steel. This combination of materials will preserve an adequate preload over the operating temperature of a typical motor, for example from about −40° C. (−40° F.) to about 105° C. (220° F.).
- The foregoing has described a motor assembly for use with a reciprocating load such as a diaphragm pump. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.
Claims (19)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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US10/550,256 US20060181168A1 (en) | 2003-04-14 | 2004-04-14 | Pump motor with bearing preload |
US12/701,936 US8096043B2 (en) | 2003-04-14 | 2010-02-08 | Method of assembling a pump motor and preloading bearings of the motor |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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US46278803P | 2003-04-14 | 2003-04-14 | |
PCT/US2004/011403 WO2004092582A2 (en) | 2003-04-14 | 2004-04-14 | Pump motor with bearing preload |
US10/550,256 US20060181168A1 (en) | 2003-04-14 | 2004-04-14 | Pump motor with bearing preload |
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US12/701,936 Continuation US8096043B2 (en) | 2003-04-14 | 2010-02-08 | Method of assembling a pump motor and preloading bearings of the motor |
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US12/701,936 Active US8096043B2 (en) | 2003-04-14 | 2010-02-08 | Method of assembling a pump motor and preloading bearings of the motor |
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US12/701,936 Active US8096043B2 (en) | 2003-04-14 | 2010-02-08 | Method of assembling a pump motor and preloading bearings of the motor |
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Also Published As
Publication number | Publication date |
---|---|
US20100132186A1 (en) | 2010-06-03 |
US8096043B2 (en) | 2012-01-17 |
WO2004092582A2 (en) | 2004-10-28 |
WO2004092582A3 (en) | 2006-04-20 |
EP1631743A4 (en) | 2006-12-20 |
CN1856925A (en) | 2006-11-01 |
CN100499316C (en) | 2009-06-10 |
JP2006524480A (en) | 2006-10-26 |
JP4699348B2 (en) | 2011-06-08 |
EP1631743A2 (en) | 2006-03-08 |
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