U.S. patent application number 10/550256 was filed with the patent office on 2006-08-17 for pump motor with bearing preload.
Invention is credited to Douglas Allan Curtis, Donald Edwin Hargraves.
Application Number | 20060181168 10/550256 |
Document ID | / |
Family ID | 33299991 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060181168 |
Kind Code |
A1 |
Hargraves; Donald Edwin ; et
al. |
August 17, 2006 |
Pump motor with bearing preload
Abstract
A electrical machine includes a housing assembly, first and
second bearings mounted in the housing assembly, and a rotor
assembly mounted in the bearings such that it 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 are secured to one of the rotor
assembly or to the housing, such that the rotor assembly is
retained in the preloaded position. The components of the
electrical machine are chosen such that this preload is maintained
over the operating temperature range of the machine.
Inventors: |
Hargraves; Donald Edwin;
(Huntersville, NC) ; Curtis; Douglas Allan;
(Troutman, NC) |
Correspondence
Address: |
ADAMS EVANS P.A.
2180 TWO WACHOVIA CENTER
CHARLOTTE
NC
28282
US
|
Family ID: |
33299991 |
Appl. No.: |
10/550256 |
Filed: |
April 14, 2004 |
PCT Filed: |
April 14, 2004 |
PCT NO: |
PCT/US04/11403 |
371 Date: |
September 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60462788 |
Apr 14, 2003 |
|
|
|
10550256 |
Sep 22, 2005 |
|
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Current U.S.
Class: |
310/90 ;
310/89 |
Current CPC
Class: |
F16C 25/083 20130101;
F16C 19/06 20130101; H02K 5/1732 20130101; Y10T 29/49012 20150115;
Y10T 29/49009 20150115; F04B 17/03 20130101; H02K 5/1735 20130101;
Y10T 29/49698 20150115; Y10T 29/49679 20150115 |
Class at
Publication: |
310/090 ;
310/089 |
International
Class: |
H02K 5/16 20060101
H02K005/16; H02K 5/00 20060101 H02K005/00 |
Claims
1. A electrical machine, comprising: a housing assembly having
first and second ends; a first bearing mounted in said housing,
said first bearing having a plurality of rolling elements disposed
between first inner and outer races; a second bearing mounted in
said housing and spaced away from said first bearing, said second
bearing having a plurality of rolling elements disposed between
second inner and outer races; a rotor assembly having first and
second ends mounted in said first and second bearings,
respectively, such that said rotor has a predetermined amount of
axial and radial play relative to said housing; and a biasing
element disposed between one of said rotor assembly or said housing
and one of said bearings, said biasing element urging said rotor
assembly to a preloaded position which eliminates said axial and
radial play, wherein each of said first inner and outer races and
said second inner and outer races is secured to one of said rotor
assembly or to said housing, such that said rotor assembly is
retained in said preloaded position.
2. The electrical machine of claim 1 wherein said first and second
outer races are secured to said housing, and said first and second
inner races are secured to said shaft.
3. The electrical machine of claim 1 wherein said biasing element
comprises a spring disposed between said rotor assembly and said
first or second inner race.
4. The electrical machine of claim 1 wherein said biasing element
comprises a spring disposed between said housing and said first or
second outer race.
5. The electrical machine of claim 1 wherein said housing assembly
comprises: 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 said
housing.
6. The electrical machine of claim 1 wherein the coefficients of
thermal expansion of said housing assembly, said bearings, and said
rotor are selected so that said rotor assembly will be retained in
said preloaded position over a temperature range of about
-40.degree. C. to about 105.degree. C.
7. The electrical machine of claim 6 wherein said bearings are
constructed from high carbon chromium steel and said housing
assembly and said rotor assembly are constructed from 400 series
stainless steel.
8. A method of assembling an electrical machine, comprising:
providing a housing having first and second ends; disposing a first
bearing in said housing, said first bearing having a plurality of
rolling elements disposed between first inner and outer races;
disposing a second bearing in said housing, said second bearing
having a plurality of rolling elements disposed between second
inner and outer races; providing a rotor assembly having a
longitudinally-extending shaft; rotatably mounting said rotor
assembly in said housing with said shaft received in said first and
second bearings, such that said rotor is in a first position in
which it has a predetermined amount of axial and radial play
relative to said housing; installing a biasing element between one
of said rotor assembly or said housing and one of said bearings,
such that said biasing element forces said rotor assembly to a
second position in which said axial and radial play is eliminated;
and securing each of said first inner and outer races and said
second inner and outer races to one of said rotor assembly or to
said housing, such that said rotor assembly is retained in said
second position.
9. The method of claim 8 wherein said first and second outer races
are secured to said housing, and said first and second inner races
are secured to said shaft.
10. The method of claim 8 wherein said biasing element comprises a
spring disposed between said shaft and said first or second inner
race.
11. The method of claim 8 wherein said biasing element comprises a
spring disposed between said housing and said first or second outer
race.
12. The method of claim 8 wherein each of said first inner and
outer races and said second inner and outer races is secured by a
method selected from the group consisting of: press fitting,
adhesive bonding, welding, or brazing.
13. An electric motor, comprising: a generally cylindrical housing
assembly having first and second ends, said 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, said first outer race being received in said first
bearing pocket; a second bearing having a plurality of rolling
elements disposed between second inner and outer races, said second
outer race being received in said second bearing pocket; a rotor
assembly including a shaft received in said first and second inner
races, such that said rotor has a predetermined amount of axial and
radial play relative to said housing; and a biasing element
disposed between one of said rotor assembly or said housing and one
of said bearings which urges said rotor assembly to a preloaded
position which eliminates said axial and radial play, wherein said
first inner and outer races are secured to said shaft, and said
second inner and outer races are secured to said housing, such that
said rotor assembly is retained in said preloaded position.
14. The electric motor of claim 13 wherein said first and second
outer races are secured to said housing, and said first and second
inner races are secured to said shaft.
15. The electric motor of claim 13 wherein said biasing element
comprises a spring disposed between said shaft and said first or
second inner race.
16. The electric motor of claim 13 wherein said biasing element
comprises a spring disposed between said housing and said first or
second outer race.
17. The electric motor of claim 13 wherein said housing assembly
comprises: 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 said
housing.
18. The electric motor of claim 13 wherein the coefficients of
thermal expansion of said housing assembly, said bearings, and said
rotor are selected so that said rotor assembly will be retained in
said preloaded position over a temperature range of about
-40.degree. C. to about 105.degree. C.
19. The electric motor of claim 18 wherein said bearings are
constructed from high carbon chromium steel and said housing
assembly and said rotor assembly are constructed from 400 series
stainless steel.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] 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.
[0004] it is another object of the invention to provide a motor
having a consistent preload under all operating conditions.
[0005] It is another object of the invention to provide a method of
assembling a motor which eliminates radial and axial play from the
bearings.
BRIEF SUMMARY OF THE INVENTION
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] According to another embodiment of the invention, the
biasing element is a spring disposed between the housing and the
first or second outer race.
[0011] 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.
[0012] 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.degree. C. to about 105.degree. C.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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
[0017] According to another embodiment of the invention, the
biasing element comprises a spring disposed between the housing and
the first or second outer race.
[0018] 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
[0019] 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.
[0020] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] 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:
[0022] FIG. 1 is a side elevational view of a ball bearing in a
rest condition.
[0023] FIG. 2 is a side elevational view of the ball bearing of
FIG. 1 in a preloaded condition.
[0024] FIG. 3 is enlarged view of a portion of the bearing of FIG.
2.
[0025] FIG. 4 is a side elevational view of a first embodiment of a
motor constructed in accordance with the present invention.
[0026] FIG. 5 is a side elevational view of a first alternative
arrangement of the components of the motor of FIG. 4.
[0027] FIG. 6 is a side elevational view of a second alternative
arrangement of the components of the motor of FIG. 4.
[0028] FIG. 7 is a side elevational view of a third alternative
arrangement of the components of the motor of FIG. 4.
[0029] FIG. 8 is a side elevational view of a second embodiment of
a motor constructed in accordance with the present invention.
[0030] FIG. 9 is a side elevational view of a first alternative
arrangement of the components of the motor of FIG. 8.
[0031] FIG. 10 is a side elevational view of a second alternative
arrangement of the components of the motor of FIG. 8.
[0032] FIG. 11 is a side elevational view of a third alternative
arrangement of the components of the motor of FIG. 8.
DETAILED DESCRIPTION OF THE INVENTION
[0033] 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 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.
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.
[0034] 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. As shown more clearly in FIG. 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. Additionally, because
of the arcuate shape of the grooves, relative axial motion of the
bearing races causes a wedging effect which prevents relative
radial motion between the inner and outer races. Thus, an axial
preload may be used to remove both axial and radial play from a
ball bearing.
[0035] Turning now to the present invention, 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. In the illustrated example the spring is a
compression-type coil spring. However, 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.
[0036] 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.
[0037] 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.
[0038] Finally, the inner race 48 of the front bearing 20 is
secured to the front shaft extension 40, and 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.
Thus, 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.
[0039] FIG. 5 illustrates a motor 110 which is a variation of the
motor 10 depicted in FIG. 4. In this instance, 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] Finally, 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. Thus, 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.
[0045] FIG. 7 illustrates a variation 310 of the motor 210. In this
instance, 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.
[0046] 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. 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 shaft 36'. In the illustrated example the
spring is a compression-type coil spring. However, 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.
[0047] 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.
[0048] 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'.
[0049] Next, 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'.
[0050] Finally, the inner races of both the front bearing 20' and
the rear bearing are secured to the shaft 36' so that no relative
motion can take place between the inner races and the shaft 36', in
a manner described above. This arrangement eliminates all axial and
radial play from the bearing and shaft mechanism.
[0051] FIG. 9 illustrates a motor 510 which is a variation of the
motor 410 depicted in FIG. 8. In this instance, 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.
[0052] 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.
[0053] First, 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.
[0054] 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.
[0055] 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'.
[0056] Finally, the inner race of the front bearing 20' is secured
to the shaft 36 and the outer race 50' of the rear bearing 22' is
secured to the housing 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.
[0057] FIG. 11 illustrates a motor 710 which is a variation of the
motor 610 depicted in FIG. 10. In this instance, 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.
[0058] 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.
[0059] 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.degree.
C. (-40.degree. F.) to about 105.degree. C. (220.degree. F.).
[0060] 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.
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