Compliantly mountable turbine cartridge assembly for gas-driven dental handpiece

A single-unit turbine cartridge assembly for a gas-driven dental handpiece includes a pair of bearing assemblies mounted on a turbine rotor shaft and a ring of resilient material around each bearing assembly. The resilient ring provides radial support for the turbine cartridge assembly within the housing of the handpiece and substantially dampens the transfer of vibration from the cartridge assembly to the handpiece during use of the handpiece. The turbine cartridge assembly may optionally include bearing axial pre-load means in association with one or more of the bearing assemblies. The turbine cartridge assembly also includes means for retaining the resilient radial support means and the bearing axial preload means, when used, in association with the bearing assemblies, so as to permit removal, and reinstallation, of the cartridge assembly as an entire unit from, and to, the housing in the dental handpiece.

BACKGROUND OF THE INVENTION 
1. Field 
Dental handpieces having gas-driven motors are well known. Of particular 
interest herein is a high-speed gas-driven dental handpiece having 
decreased noise and improved vibration damping characteristics. 
2. State of the Art 
A dental handpiece of a type having a high-speed gas-driven motor, of which 
the turbine rotor and bearings are replaceable as a multi-piece unit 
within the motor housing, is described in U.S. Pat. No. 3,074,167 to 
Turchi et al. A rotor of a high-speed motor of this type will rotate at 
speeds of 250,000 to 400,000 rpm, or more, during use of the handpiece by 
a dentist. Significant amounts of vibration and noise may be transmitted 
from the motor to the handle portion during use of a high-speed handpiece 
having a rotor bearing cage in direct contact with the handpiece motor 
housing, such as shown in the Turchi et al U.S. Pat. No. 3,074,167 patent. 
Vibration and noise even in small amounts can be quite disturbing to 
dentist and patient alike, and may be especially disturbing when, at 
certain critical rotor operating speeds, resonance effects greatly enhance 
or amplify the noise or vibration originating from the gas-driven motor. 
A high-speed handpiece having reduced vibration and noise transmitting 
characteristics is disclosed in U.S. Pat. No. 3,499,223 to Lieb et al, 
wherein vibration damping rings fabricated of non-metallic or rubbery 
materials are interposed between the metallic rotor bearings and a 
metallic motor housing. These vibration damping rings are described as 
insertable within a gas-driven motor housing separately from the turbine 
rotor-and-bearing assembly. A disadvantage of this arrangement is that 
during removal and reinstallation of a turbine assembly by a handpiece 
user in a dental office one or both of the vibration damping rings may 
frequently become lodged in the motor housing, with resultant difficulty 
following in the removal of the ring. Also, reinstallation of each ring 
separately from the turbine-and-bearing assembly is a time-consuming chore 
requiring a relatively high degree of care to avoid improper orientation 
or seating of the ring in the motor housing. 
Another problem associated with proper installation or positioning of a 
turbine-and-bearing assembly within a gas-driven motor housing is in 
obtaining proper rotor alignment and static pre-loading of the bearings 
within the housing. One aspect of proper rotor alignment is the degree of 
concentricity maintained between the motor housing axis and the axis of 
rotation of a dental bur which is mounted by its shank within the turbine 
cartridge assembly rotor shaft. The degree of concentricity is, in turn, 
related to bur run-out, that is, the distance of movement of a rotating 
bur from its theoretical axis as measured in a plane perpendicular to the 
rotor shaft axis, the plane intersecting the tip of the bur. Typically, a 
dental bur has some imbalance as a result of manufacture or because of an 
irregular configuration of the bur work surface. The combination of poor 
concentricity and bur imbalance may provide a considerable amount of 
vibration during use of the handpiece especially at or near the critical 
frequency of rotation of the turbine. 
Improper axial or radial alignment of the rotor shaft with respect to the 
motor housing, or the application of too little or too much static 
pre-loading to the rotor shaft bearings, may also lead to excessive noise 
and vibration causing pre-mature wear and failure of the bearings. The 
problem of misalignment may be especially acute with a handpiece having 
separately-installed vibration damping rings, or spring-like bearing 
pre-loading elements, or both, where special care must be taken to prevent 
distortion of the rings, misalignment of the rotor, improper static 
pre-loading of the bearings, or loss of the various separately-installed 
components. 
There is need, therefore, for a high-speed gas-driven dental handpiece 
having a turbine-and-bearing assembly which can be easily removed and 
reinstalled in a motor housing as a unitary assembly which contains all of 
the various parts for achieving proper radial and axial alignment to 
provide a high degree of concentricity, and which turbine cartridge 
assembly when installed in a handpiece motor housing may provide a proper 
degree of static preloading to the rotor shaft bearings. 
SUMMARY OF THE INVENTION 
A turbine-and-bearing assembly for a high speed gas-driven motor of a 
dental handpiece of the present invention provides an advantage of 
improved ease of removal and reinstallation of the turbine assembly from a 
motor housing as a unitary assembly. Secondly, the turbine assembly of 
this invention is easily alignable within a motor housing in a manner that 
provides a proper degree of pre-loading force to the rotor shaft bearings 
for minimum wear of the bearings. The turbine assembly of this invention 
when installed in a high-speed dental handpiece provides low transmission 
of vibration from the motor housing to the handle portion of the handpiece 
and reduced bur run-out. 
These and other advantages are provided by a turbine cartridge assembly 
which is removably positionable as a unit within a housing of a gas-driven 
motor of a dental handpiece. The motor housing is typically located in one 
end portion of a dental handpiece and is defined by a substantially 
cylindrical side wall and a pair of oppositely disposed end walls 
transverse to the side wall, with means for supporting a turbine cartridge 
assembly located on portions of the side wall and end walls. The turbine 
cartridge assembly may in one embodiment comprise a rotor shaft having a 
plurality of vanes thereon, the rotor shaft having an axis of rotation 
substantially coincident with the axis of the cylindrical side wall of the 
motor housing, a first bearing assembly comprising an inner race fixed to 
the rotor shaft, an outer race, and a plurality of movable bearing 
elements frictionally engaged with and confined between the inner race and 
the outer race, a second bearing assembly comprising an inner race fixed 
to the rotor shaft in spaced relationship with the inner race of the first 
bearing assembly, an outer race, and a plurality of movable bearing 
elements frictionally engaged with and confined between the inner race and 
the outer race of the second bearing assembly, radial support means 
associated with each of the first and second bearing assemblies, the 
radial support means providing radial support for the turbine cartridge 
assembly when in contact with the substantially cylindrical side wall of 
the motor housing, rigid axial support means associated with the outer 
race of the first bearing assembly for axially supporting the first 
bearing assembly outer race upon turbine cartridge support means located 
on an end wall portion of the housing, bearing pre-loading means 
comprising flexible axial support means associated with the outer race of 
the second bearing assembly for yieldingly supporting the outer race upon 
turbine cartridge support means located on an end wall portion of the 
housing to provide a controlled axial force on the outer race of the 
second bearing assembly, which force is transmitted through the rotor 
shaft to the first bearing assembly to provide pre-loading to the first 
bearing assembly, and means for retaining the radial support means and the 
flexible axial support means upon the outer race of the second bearing 
assembly. The rigid axial support means and the flexible axial support 
means coact with the turbine cartridge support means on the housing end 
wall to provide axial pre-loading of the first and second bearing 
assemblies when the turbine cartridge assembly is operatively positioned 
within the motor housing. 
The aforementioned rigid axial support means and flexible axial support 
means comprise means for yieldingly coacting with the turbine cartridge 
assembly support means in the motor housing of a dental handpiece to 
provide axial pre-loading of the first and second bearing assemblies when 
the turbine cartridge assembly is operably positioned within the motor 
housing. It is an advantage of the invention that various degrees of 
pre-loading may be provided for a turbine cartridge assembly by the axial 
pre-load means to compensate for varying degrees of tolerances that exist 
between components of one bearing assembly and another. Thus bearing 
assemblies may be employed which have a broader range of component 
tolerances or "stop" between bearing components thereby providing an 
advantage in economy of manufacture. 
It is another feature of the invention that the entire turbine cartridge 
assembly is adapted for placement in, and removal from, the housing as a 
unitary assembly so that during field replacement of the turbine cartridge 
assembly, the various means for obtaining proper rotor alignment, bearing 
pre-load or vibration damping are retained on the turbine cartridge 
assembly and need not be separately removed from, or inserted in, the 
handpiece motor housing. 
The rigid axial support means typically comprises a flange extending 
radially outwardly from and integrally formed with the outer race of each 
of the first and second bearing assemblies, although various other 
constructions affording a rigid flange, or the equivalent thereof, may be 
provided. The flexible axial support means typically includes at least one 
resilient spacer member circumferentially disposed about at least one of 
the bearing assembly outer races. The resilient spacer member, interposed 
between the turbine cartridge support means located on the motor housing 
end walls and the rigid axial support means of the outer race of one of 
the bearing assemblies, is adapted to transmit a controlled compression 
force therebetween so as to urge the outer race toward the rotor vanes in 
a direction substantially parallel with the axis of the rotor shaft. It is 
preferred that the resilient spacer member have a spring constant 
sufficient to provide a static pre-load to each of the bearing assemblies 
in the axial direction in the range of about 0.5 to about 1.5 pounds when 
the turbine cartridge assembly is operably positioned within the motor 
housing. 
The turbine cartridge assembly also includes means for retaining the 
flexible axial support means and other support components upon the outer 
race of the second bearing assembly and may also include means for 
retaining the rigid axial support means and other support components upon 
the outer race of the first bearing assembly, particularly where the rigid 
axial support means is not integrally formed with the outer race. 
Retention of these various support means upon each of the bearing assembly 
outer races allows removal and reinstallation of all components of the 
turbine assembly as a unitary cartridge, which thus precludes the loss of 
the support components during handling of the turbine cartridge assembly. 
The turbine cartridge assembly includes radial support means which provide 
radial support for each of the first and second bearing assemblies against 
the substantially cylindrical side wall of the housing. In addition to 
providing proper radial positioning of the turbine cartridge assembly with 
respect to the motor housing side wall, it is desirable that the radial 
support means ideally have mechanical properties which inhibit the 
transmission of vibration from a rotating turbine cartridge assembly to 
the motor housing. In preferred embodiments of the invention, the radial 
support means comprises a ring of resilient material interposed between 
each of the first and second bearing assembly outer walls and a portion of 
the housing cylindrical side wall adjacent each of the bearing assemblies. 
These resilient rings are characterized in providing sufficiently rigid 
radial support of the turbine cartridge assembly while, at the same time, 
providing means for damping or reducing the transmission of vibration 
between the turbine bearings and the motor housing. 
A dental handpiece having a turbine cartridge assembly of this invention 
which includes radial support means comprising resilient, 
vibration-damping rings may be described as compliantly mounted or 
suspended within the handpiece motor housing. 
A significant advantage is provided by a turbine cartridge assembly of this 
invention including radial support means comprising resilient members 
having a particular physical characteristic, as hereinafter defined. In 
some conventional handpieces having metallic or substantially 
non-resilient supports between the turbine bearings and the motor housing, 
there may be a very low degree of resilience, as measured by spring rate, 
of about 5000 pounds per inch. This very high spring rate provides for 
little damping of vibration between the bearing and the motor housing. In 
the present invention, resilient elements are utilized between the turbine 
cartridge bearing assemblies and the motor housing wall, which resilient 
elements have spring rates of 80 to 100 pounds per inch. This greatly 
reduced spring rate provides improved damping of vibration which is 
characteristic of the compliantly mountable turbine cartridge assembly of 
this invention. 
The radial support means of the turbine cartridge assembly of the invention 
may, however, in a lesser preferred embodiment, comprise substantially 
non-resilient members such as provided by the metallic outer wall of each 
of the bearing assembly outer races. 
In another embodiment of the invention, the turbine cartridge assembly may 
comprise a rotor shaft having a plurality of vanes thereon, the rotor 
shaft defining an axis of rotation, a first bearing assembly comprising an 
inner race fixed to the rotor shaft, an outer race, and a plurality of 
movable bearing elements frictionally engaged with the confined between 
the inner race and the outer race, a second bearing assembly comprising an 
inner race fixed to the rotor shaft, an outer race, and a plurality of 
movable bearing elements frictionally engaged with and confined between 
the inner race and the outer race of the second bearing assembly, radial 
support means associated with each of the first and second bearing 
assemblies, the radial support means comprising a resilient member 
interposed between each of the bearing assemblies and an adjacent portion 
of the housing side wall, the radial support means providing 
vibration-damping radial support for the turbine cartridge assembly upon 
the substantially cylindrical side wall of a handpiece housing, and 
retaining means mounted on each of the bearing assembly outer races for 
retaining the radial support means upon the turbine cartridge assembly. 
Though this embodiment lacks flexible support means or the aforementioned 
means for yieldingly coacting with the turbine cartridge assembly support 
means, which provide axial static pre-loading of the bearing assemblies, 
the inclusion of radial support means having a resilient, 
vibration-damping nature provides a compliantly mountable or suspendable 
turbine cartridge assembly for a handpiece housing. Inasmuch as there is a 
lack of the aforementioned axial pre-load means, the turbine cartridge 
assembly may require bearing assemblies having component tolerances which 
provide a limited amount of bearing axial end play to ensure low vibration 
or noise levels.

Illustrated in FIG. 1 is a dental handpiece 10 including a barrel-shaped 
handle portion 11 having an outer wall 12 with flutes 13 which provide a 
hand-grippable surface. Handle portion 11 has at one end thereof an 
elongated neck 14 joined to handle portion 11 at a knuckle 15. Neck 14 
terminates in head 16 having a gas-driven motor 17 provided by a motor 
housing 18 and turbine cartridge assembly 19, as depicted in FIG. 2. Motor 
housing 18 is defined by a substantially cylindrical inner side wall 20, 
having an axis lying generally transverse to the axis of neck 14, and by a 
pair of oppositely disposed end walls transverse to side wall 20. One 
housing end wall 21 is integrally formed with housing side wall 20 within 
head 16. The other housing end wall is furnished by end cap 22 which has 
an annular-shaped flange 23 extending into housing 18 in a generally axial 
direction. Flange 23 has an exteriorly threaded portion 24 which engages 
an interiorly threaded portion 25 on an adjacent portion of side wall 20. 
End cap 22 contains an orifice 26 which, when end cap 22 is threadedly 
secured to housing side wall 20, is axially aligned with an orifice 27 in 
oppositely disposed end wall 21. 
Integrally formed along a portion of housing side wall 20 near end wall 21 
is an annular-shaped ledge or shoulder 28 which extends radially inwardly 
toward the axis of housing 18. Shoulder 28 comprises a part of end wall 21 
and provides a portion of the means for supporting turbine cartridge 
assembly 19 within housing 18. At the opposite end of housing 18, annular 
flange 23 of end cap 22 provides an annular-shaped shoulder 29 which also 
comprises a portion of the means for supporting turbine cartridge assembly 
19 within housing 18. 
Turbine cartridge assembly 19 comprises an elongated rotor shaft 30 having 
an axis of rotation that is substantially coincident with the axis of 
motor housing 18. Rotor shaft 30 has an axial bore 31 extending the length 
thereof. There is an interiorly threaded portion 32 at the end of rotor 
shaft 30 adjacent end cap 22. At its opposite end, rotor shaft 30 has a 
tapered portion 33 which slopes inwardly toward the axis of rotor shaft 
30. Contained within rotor shaft bore 31 is a collet 34 having at one end 
an exteriorly threaded portion 35 which engages threaded portion 32 of 
rotor shaft 30. At its opposite end, collet 34 has a plurality of jaws 36 
for gripping a shank 37 of a work tool when collet 34 is threaded into 
rotor shaft 30. Additional details and advantages of construction of a 
dental handpiece having the illustrated collet may be found in U.S. Pat. 
No. 3,120,706 to Turchi et al, the disclosure of which is incorporated 
herein by reference. A description of means for inserting and removing a 
work tool, such as a dental bur, into and from collet 34 may be found in 
U.S. Pat. No. 3,947,966 to Lieb et al. 
Rotor shaft 30 is journalled upon a pair of first and second bearing 
assemblies 38 and 39, respectively, which are in axially spaced 
relationship along rotor shaft 30. It should be noted that the terms 
"first" and "second" designating bearing assemblies 38 and 39 are for 
convenience of discussion only, and that either bearing assembly could be 
designated "first" or "second" since the designation is entirely 
arbitrary. Hence, the following descriptions relating to the "first 
bearing assembly" may, as well, relate to the "second bearing assembly", 
and vice versa. 
First bearing assembly 38 comprises a ring-like inner race 40, which is 
fixedly journalled upon a portion of rotor shaft 30 adjacent end cap 22, 
and a ring-like outer race 41 spaced therefrom. Inner race 40 and outer 
race 41 provide a bearing housing in which a plurality of movable ball 
bearing elements 42 can be confined between and frictionally engaged with 
races 40 and 41. Second bearing assembly 39 similarly comprises an inner 
race 43, an outer race 44 and movable ball bearing elements 45 confined 
and frictionally engaged therebetween. Inner race 43 is fixedly journalled 
upon rotor shaft 30 in spaced relationship with inner race 40 of first 
bearing assembly 38, that is, inner race 43 of second bearing assembly 39 
is journalled upon a portion of rotor shaft 30 closer to end wall 21. 
Alternatively, inner races 40 and 43 could as well be integrally formed 
with rotor shaft 30. 
Rotor 46 including a plurality of vanes 47 radiating outwardly from rotor 
shaft 30 is fixedly journalled upon rotor shaft 30 between first and 
second bearing assemblies 38 and 39. Vanes 47 impart rotational movement 
to rotor shaft 30 when a high velocity gas stream impinges upon vanes 47, 
as is well known in the art. A suitable high velocity gas stream may be 
provided from an external source of compressed air (not shown) connected 
to passageway 48 within handle portion 11, which passageway 48 is in 
communication with motor housing 18 by means of inlet port 49 in motor 
housing side wall 20. An exhaust port 50 in another portion of side wall 
20 spaced from inlet port 49 provides communication between motor housing 
18 and exhaust passageway 51. Exhaust air flows from the motor housing via 
port 50 and the hollow portions of handpiece 10 within neck 14 and handle 
portion 11 during use of the handpiece. 
Outer races 41 and 44 of first and second bearing assemblies 38 and 39, 
respectively, each have substantially cylindrically shaped outer walls 52 
and 53 facing in a direction radially outwardly of the axis of rotor shaft 
30. When turbine cartridge assembly 19 is positioned within motor housing 
18, the face of each of convex outer walls 52 and 53 is substantially 
concentric with the portions of cylindrically-shaped concave housing side 
wall 20 adjacent thereto. Outer wall 52 of first bearing assembly outer 
race 41 has a flange 54 integrally formed as the edge portion thereof 
closer to second bearing assembly 39. Flange 54 extends radially outwardly 
from the face of outer wall 52 with respect to the axis of rotor shaft 30. 
Preferably, flange 54 extends circumferentially about outer wall 52 to 
provide an annular ledge or shoulder 55. Similarly, outer wall 53 of 
second bearing assembly outer race 44 has a flange 56 integrally formed as 
the edge portion thereof closer to first bearing assembly 38. Flange 56 
extends radially outwardly from the face of outer wall 53 with respect to 
the axis of rotor shaft 30. Flange 56 preferably extends circumferentially 
about outer wall 53 to provide an annular ledge or shoulder 57. 
Adjacent flange shoulder 55 of first bearing assembly 38 is a flat washer 
58 having an annular or ring-like shape, which washer 58 lies 
circumferentially about outer wall 52. The inner diameter of washer 58 is 
less than the outer diameter of flange shoulder 55, as measured in a plane 
substantially perpendicular to the axis of rotor shaft 30, while the outer 
diameter of washer 58 is greater than the outer diameter of flange 
shoulder 55. A ring-like flat washer 59 of construction similar to washer 
58 lies circumferentially about outer wall 53 near flange shoulder 57 of 
second bearing assembly 39. 
Flat washers 58 and 59 provide rigid support means for supporting turbine 
cartridge assembly 19 upon annular-shaped shoulders 29 and 28, 
respectively, located on end cap 22 and side wall 20 of motor housing 18, 
when turbine cartridge assembly 19 is operably positioned within housing 
18. Each of flat washers 58 and 59 tends to prevent movement of outer 
races 41 and 44, respectively, in opposite directions away from rotor 
vanes 47 along the axis of rotor shaft 30. 
The rigid axial support means may be provided by other constructions in 
addition to those described above. For example, as shown in FIG. 6, 
grooves 80 and 81 each run circumferentially about outer walls 52 and 53, 
respectively, with each of the grooves lying in a plane substantially 
perpendicular to the axis of rotor shaft 30. Within each of grooves 80 and 
81 is a snap ring 82 and 83, respectively, retained within the grooves, 
and in rigid connection with the respective outer races, by the spring 
bias of the snap ring. Snap rings 82 and 83 provide shoulders 84 and 85, 
respectively, extending radially outwardly of outer race outer walls 52 
and 53, respectively. Shoulders 84 and 85 each have an outer diameter in 
the radial direction sufficient to provide rigid axial support for the 
turbine cartridge assembly upon annular shoulders 29 and 28, respectively. 
Another variation of the rigid axial support means is depicted in FIG. 7. 
Integrally formed with bearing assembly outer race 41 is a flange 86 which 
has an outer diameter in the radial direction sufficient to define a 
shoulder 87 which provides axial support for turbine cartridge assembly 19 
upon end wall shoulder 29 of motor housing 18. Flange 86 thus provides 
rigid axial support like the combination of flange 55 and flat washer 58 
depicted in FIG. 3, for example. 
As depicted in FIG. 2, there is provided in association with second bearing 
assembly 39 a resilient spacer member comprising a wavey spring washer 60 
interposed between flange shoulder 57 and flat washer 59. Spring washer 60 
has a substantially sinuous configuration and thus provides a spring-like 
thrust tending to urge outer race 44 toward outer race 41 in an axial 
direction. With turbine cartridge assembly 19 operably positioned within 
housing 18, flat washer 59 of second bearing assembly 39 is supported by 
shoulder 28 located on a portion of housing side wall 20. A reaction force 
from shoulder 28 through flat washer 59 opposes the spring compression 
force of spring washer 60. 
Likewise, other embodiments of the turbine cartridge assembly of the 
invention may have a spring washer 60 associated with second bearing 
assembly 39. As shown in FIG. 5 spring washer 60 is interposed between 
shoulder 85 of snap ring 83 and flat washer 59. In the turbine cartridge 
assembly of FIG. 7, spring washer 60 may be interposed between flange 
shoulder 57 and end wall shoulder 28 when the turbine cartridge assembly 
is operably positioned within motor housing 18. In each of these 
constructions, a reaction force is transmitted between a portion of 
housing end wall 21 and second bearing assembly outer race 44. 
Total axial loading of first and second bearing assemblies 38 and 39 may be 
accomplished with a single wavey washer 60 positioned in association with 
second bearing assembly 39 as depicted in FIGS. 2, 5 and 7. The 
illustration of transmitted forces within turbine cartridge assembly 19, 
as indicated by the arrows in FIG. 2, demonstrates the manner in which 
axial pre-loading of both bearing assemblies of turbine cartridge assembly 
19 may be accomplished by a single spring washer 60. The pre-load 
compression force exerted by wavey washer 60 is transmitted through outer 
race 44 of second bearing assembly 39 to ball bearing element 45 then to 
inner race 43 affixed to one end of rotor shaft 30. At the other end of 
rigid rotor shaft 30, the pre-load force is transmitted from the rotor 
shaft through inner race 40 of the first bearing assembly to ball bearing 
element 42 and then to outer race 41 which is restrained from axial 
displacement away from rotor vanes 47 by flat washer 58 supported upon 
annular shoulder 29 of end cap 22. Axial pre-loading is likewise achieved 
by a single spring washer 60 in the turbine cartridge assemblies of FIGS. 
5 and 7. 
In another embodiment of the turbine cartridge assembly as depicted in FIG. 
4, resilient spacer members comprising wavey spring washers 61 and 60, 
respectively, are associated with each of first and second bearing 
assemblies 38 and 39. Each of wavey washers 60 and 61 has a sinuous 
configuration and provides a spring-like thrust tending to urge outer 
races 41 and 44 toward each other in the axial direction. The two spring 
washers 60 and 61 thus cooperate to provide a total pre-loading of the 
first and second bearing assemblies. 
Typically, a suitable spring washer is fabricated of materials such as 
spring steel or phosphor bronze and will have dimensions and a spring 
constant adapted to the particular configuration and desired degree of 
axial play of the bearing assemblies of a turbine cartridge assembly. It 
is preferred that in either embodiment illustrated in FIG. 2 and FIG. 3 
the total axial pre-loading of the first and second bearing assemblies, as 
provided by one or more wavey washers, should be in the range of about 0.5 
to about 1.5 pounds, which provides a good balance between low noise and 
vibration characteristics and long bearing life. 
Although the described axial pre-loading means may be used successfully in 
a turbine cartridge assembly designed to have bearing assemblies which are 
in direct frictional contact with a motor housing side or end walls, it is 
preferred that resilient spacer rings be interposed between the bearing 
assemblies and adjacent portions of housing side wall 20 to provide radial 
support and a compliant mounting or suspension for turbine cartridge 
assembly 19. As illustrated in FIG. 2, a pair of resilient rings 62 and 
63, such as commercially available O-rings fabricated of rubbery material, 
lie circumferentially about outer walls 52 and 53 of the outer races of 
first and second bearing assemblies 38 and 39, respectively. Preferably, 
each of O-rings 62 and 63 has an inner diameter in the radial direction 
with respect to the axis of rotor shaft 30 which is slightly less than the 
outer diameter of outer walls 52 and 53 so that each of O-rings 62 and 63 
is in a slightly stretched configuration around its respective outer race. 
Each of resilient O-rings 62 and 63 will have an outer diameter slightly 
greater than the diameter of the housing at the portion of the housing 
side wall adjacent to the O-ring. Thus when turbine cartridge assembly 19 
is positioned within housing 18, O-rings 62 and 63 become compressed in 
the radial direction. This radial compression of the O-rings provides both 
a sleeve or frictional fit and suitable alignment of turbine cartridge 
assembly 19 within housing 18. In addition to inhibiting radial 
displacement of the turbine cartridge assembly, the O-rings inhibit 
transfer of vibration from the cartridge assembly to the handle portion 
during use of the handpiece. 
The O-rings 62 and 63 may be fabricated of practically any elastic or 
resilient material that has good vibration and noise damping properties 
and which resists high temperature and steam conditions typical of 
repeated autoclave cycles required for sterilization during the useful 
life of the dental instrument. Satisfactory materials include, for 
example, neoprene elastomer, ethylenepropylene elastomer, fluorocarbon 
elastomer and butadiene/acrylonitrile elastomer (known commercially as 
Buna-N rubber). 
A significant advantage of a turbine cartridge assembly of this invention 
is provided by the ease of removal and replaceability of the turbine 
cartridge assembly from and to a dental handpiece, which is attributable 
to the feature of all of the components of the turbine cartridge assembly 
being removed or replaced as a unitary assembly. The aforementioned one or 
more spring washers for effecting proper bearing pre-loading and the 
resilient O-rings which provide vibration and noise damping are all 
retained on the turbine cartridge assembly, thereby precluding removal or 
reinsertion of these parts separately from other turbine components. 
Retention of the spring washers or the O-rings on the turbine cartridge 
assembly may be accomplished by cooperation of bearing outer race flanges 
54 and 56 with various means associated with the outer race of each 
bearing assembly. For example, in some constructions each of O-rings 62 
and 63 may have a sufficiently secure friction fitting with the respective 
outer wall of first and second bearing assembly outer races 41 and 44 to 
prevent axial movement of one or more spring washers toward the ends of 
rotor shaft 30. More likely, each of first and second bearing assemblies 
38 and 39 will have additional retaining means for keeping both the one or 
more spring washers and the O-rings on turbine cartridge assembly 19 as 
shown, for example, in each of the embodiments of FIGS. 2, 3 and 4. The 
retaining means comprise snap rings 64 and 65 which rest in grooves 66 and 
67 running circumferentially about outer walls 52 and 53 of first and 
second bearing assembly outer races 41 and 44, respectively. Snap rings 64 
and 65 retain flat washers 58 and 59, spring washer 60 (and 61 of the 
embodiment of FIG. 4) and O-rings 62 and 63 upon their respective bearing 
assemblies, so that none of these components become lost or misaligned 
during removal or replacement of the turbine cartridge assembly from the 
motor housing. 
As another aspect of the invention, a turbine cartridge assembly may lack 
the aforementioned bearing axial pre-load means as provided, for example, 
by one or more spring washers interposed between one or more of the 
bearing assemblies and adjacent portions of the housing end walls. For 
example, as shown in FIG. 6, each of first and second bearing assemblies 
38 and 39, respectively, has rigid axial support means which provide 
support for turbine cartridge assembly 19 upon end wall shoulders 29 and 
28, respectively, when turbine cartridge assembly 19 is operably 
positioned within motor housing 18. The rigid support means is depicted as 
comprising snap rings 82 and 83 rigidly connected to bearing assembly 
outer races 41 and 43 by the spring tension of each of snap rings 82 and 
83, respectively, within each of grooves 80 and 81. It should be 
understood, however, that any of the other described rigid axial support 
means of FIGS. 2, 3, 4, 5 and 7, or combinations thereof, could be 
utilized as well. Turbine cartridge assembly 19 of FIG. 6 is characterized 
as compliantly mountable, though lacking axial pre-loading means, inasmuch 
as there is provided radial support means which comprise resilient O-rings 
62 and 63. 
Each of bearing assemblies 38 and 39 may also contain shield rings 68 and 
69 resting in grooves 70 and 71, respectively, running circumferentially 
about inner walls 72 and 73 of first and second bearing assembly outer 
races 41 and 44, respectively. The purpose of shield rings 68 and 69 is to 
aid in retention of lubricant within and around each of ball bearing 
retainers 74 and 75 and to retard contamination of the bearings by entry 
of particulate matter into the bearing cages. 
While this invention has been described with reference to specific 
embodiments thereof, it should be understood by those skilled in this art 
that various changes may be made and equivalents may be substituted 
without departing from the true spirit and scope of the invention. All 
such modifications are intended to be within the scope of the claims 
appended hereto.