Compressed-air dental motor

A compressed-air dental motor includes a housing, a rotor, a compressed air inlet conduit supplying compressed air for placing the rotor into rotation, and a rotor shaft in the rotor connectable with a work tool, such as a drill. A valve member in the housing associated with the compressed-air inlet conduit is adapted to vary the inlet of compressed air for each unit of time, and an adjusting device is provided for controlling the valve member. The rotor shaft includes an axially displaceable component for controlling the valve member in direct mechanical dependence upon the torque at the work tool so as to form the adjusting device into a torque-dependent adjusting device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a compressed-air dental motor, consisting 
of a housing having a rotatably supported rotor arranged therein adapted 
to be set into rotation through compressed air introduced into the housing 
through the intermediary of a compressed-air inlet conduit; which includes 
a rotor shaft connectable with a tool, for instance a drill, wherein the 
compressed-air inlet conduit is associated with a valve arrangement 
located in the housing which is adapted to vary the compressed air infeed 
for each unit of time and which is controllable by means of a setting 
mechanism. 
2. Discussion of the Prior Art 
The compressed-air motor, for example, may in accordance with German 
laid-open patent application No. 19 41 159 be constructed as a turbine 
which has a rotor provided with blades; or pursuant to German published 
patent application No. 12 32 789 as a piston motor having a rotor provided 
with cylinders for pistons, for instance in the form of balls; or pursuant 
to German laid-open patent application No. 23 04 666 as a vane motor 
having a rotor which is provided with slits for receiving radially movable 
vanes. 
In the compressed-air motor which has become known from German laid-open 
patent application No. 19 41 159, which is constructed as a turbine with a 
rotor equipped with blades wherein the compressed-air motor is only 
similar to the above-mentioned types. The setting mechanism consists of an 
electrical inductance coil located within the motor housing, in which 
there are induced voltage shocks through permanent magnets which are 
inserted in the rotor. At the loading of the work tool, the rotational 
speed of the rotor will reduce. This reduction in the rotational speed is 
transmitted through the inductance coil to a switch box arranged 
externally of the motor which includes an electrical control circuit, in 
the form of electrical amplitudes, and which emits an actuating amplitude, 
so as to be able to control in an electromagnetic manner the valve 
arrangement which is located within the compressed-air inlet conduit, also 
similarly arranged externally of the motor, for the purpose of varying the 
compressed air inlet to the motor for each unit of time. The arrangement, 
especially the switch box externally of the motor, demands special spatial 
requirements. Moreover, this known compressed air motor can only be 
employed in locations in which there is available an electrical 
connection. 
In the compressed-air motor of the above-mentioned type which has become 
known through German published patent application No. 12 32 789, which is 
constructed as a piston motor with cylinders for pistons which, for 
example, are shaped as spheres, and, in a space-saving manner with the 
valve arrangement being located within the housing, the rated speed of the 
motor is presettable by varying the cross-section of the outlet aperture 
of the exhaust air, in effect, without necessity for an electrical 
connection. The exhaust air conduit includes a branch conduit which leads 
to a diaphragm chamber possessing a diaphragm which forms the adjusting 
arrangement, wherein the diaphragm exerts an effect on a slide valve which 
forms the valve arrangement. The adjusting arrangement which is 
constructed in this manner has the function thereof dependent upon the set 
cross-section of the exhaust air outlet aperture and, consequently serves 
only for the stabilizing of the rated speed of the motor. Particularly at 
a lower set rated speed, due to dependence upon the cross-section of the 
exhaust air outlet aperture it is not possible to obtain an increase in 
the torque at the loading of the work tool, since the therefore required 
additional compressed-air quantity to be introduced for each unit of time 
after passage through the displacement volume of the motor cannot pass as 
exhaust air through the mentioned cross-section of the exhaust air outlet 
aperture, thus possibly leading to the stalling of the motor. For the 
remainder, this known arrangement can only be employed with closed, or 
effectively, sealingly constructed types of air motors, but not with 
openly constructed compressed-air motors, such as are represented by vane 
motors, in which the rotor is set into rotation through "relaxing." 
The vane motor which has become known through German laid-open patent 
application No. 23 04 666 does not at all include a valve arrangement 
which is controllable through a setting arrangement for varying the 
compressed air infeed for each unit of time, as a result of which this 
motor, which belongs to an entirely different class of construction, will 
stall upon the loading of the work tool. 
The present invention thus proceeds as an improvement over the 
compressed-air motor which has become known from Germain laid-open patent 
application No. 12 32 789. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a 
compressed-air dental motor of the above-mentioned type in which, while 
retaining the avoidance of a particular spatial requirement and a spatial 
electrical connection, ensures an increase in the torque put out by the 
motor dependent upon the magnitude of an occurring loading of the work 
tool, for example, a drill, so as to avoid, for instance, the stalling of 
the drill in the tooth during the drilling out of dental cavities, which 
would be uncomfortable to the patient, and particularly also for 
compressed-air motors which are constructed as vane motors. 
The advantages attained through the present invention can be essentially 
ascertained in that the axially slideable component serving for the 
control of the valve arrangement, independently of the cross-section of 
the exhaust air outlet aperture, is caused to be directly axially 
displaced by the loaded work tool for the purpose of controlling the valve 
arrangement, so that the proposed construction is also suitable for 
compressed-air motor types which are not closed, such as vane motors. Due 
to the independence from the size of the cross-section of the exhaust air 
outlet aperture, even at lower rated motor speeds is there achieved an 
effective increase in the torque. In this manner there is afforded that 
the compressed-air quantity introduced for each unit of time is 
automatically regulated to the torque demanded at the work tool, when 
there is required at the work tool a larger torque in the case of the 
loading thereof then that which is produced by the motor at its rated 
speed.

DETAILED DESCRIPTION 
The compressed-air dental motor 1, which is constructed as a vane motor, 
consists of a sleeve-shaped housing 2 which forms the stator in which 
there is arranged a rotatably supported rotor 4 adapted to be set into 
rotation by means of compressed air introduced into the housing through a 
compressed-air inlet conduit 3; wherein the rotor includes a rotor shaft 6 
connectable to a work tool 5, for example, a drill. The rotor 4 is 
supported within housing 1 in the endwise housing closures 7 and 8 by 
means of ball bearings 9, 10. The axis of rotation D of the rotor 4 
extends in parallel relative to the axis A of the circular cylindrical 
inner wall 11 of an inner stationery housing insert 60 and is offset with 
respect to the latter. 
Radially movably supported in longitudinal slits 12 of the rotor 4 are 
vanes 13 which have their outer ends 14 extend towards the circular 
cylindrical inner wall 11. 
Openings 15, 16, and 17 communicate with the displacement chamber 18 of the 
motor 1 located between the rotor 4 and the circular cylindrical wall 11. 
As long as the opening 15 is subjected to compressed air and as a result 
acts as an air inlet aperture, the openings 16, 17 are air outlet 
apertures. When in contrast therewith, for the purpose of the subsequently 
explained change in the direction of rotation, the opening 16 is subjected 
to compressed air and as a result acts as an air inlet aperture, the 
openings 15, 17 become air outlet apertures. Thereby, the opening 17 
always remains an air outlet aperture. Upon subjecting the motor 1 to 
compressed air, the last-mentioned enters through the air inlet aperture, 
for example opening 15, into the displacement chamber 18 and pushes the 
closest positioned vane 13 which is the furthest extended from the rotor 
4, ahead thereof, so that the rotor 4 begins to rotate and the next vane 
13 is subjected to the compressed air. The exhaust air escapes into the 
open through the air outlet apertures, for example openings 16, 17 through 
the exhaust air conduit 19 the last mentioned of which, such as the 
compressed-air inlet conduit 3, is arranged in a flexible supply hose S 
leading to the motor 1. The rotational speed of the vane motor may, for 
example, be approximately 20,000 to 100,000 r.p.m. 
The motor 1, at the work tool-sided end thereof, includes an extension 20 
for insertion into a receiving aperture of a dental handpiece 21 which is 
formed as an attachment. The handpiece 21 is in a known and therefore not 
illustrated manner, detachably connectable with the compressed-air motor 
1. In the formation of this connection, a drive shaft 22 which arranged 
interiorly of the handpiece 21 also comes into engagement with the rotor 
shaft 6 of the motor 1. The drive shaft 22 sets the work tool 5 into 
rotation through the intermediary of a plurality of gears 23 or the like 
which are arranged at angles relative to each other. 
The compressed-air inlet conduit 3 has a valve arrangement 24 associated 
therewith which varies the introduced compressed air quantity for each 
unit of time, which is located interiorly of the housing 2 and is 
controllable through an adjusting arrangement 25. The adjusting 
arrangement 25 is located intermediate the rotor 4 and the area of the 
rotor shaft 6 at the work tool end. 
In order that the adjusting arrangement 25 torque-dependently responds to 
the loading of the work tool 5 extending above the normal loading, the 
rotor shaft 6 is provided with an axially displaceable component 26 which 
controls the valve arrangement 24 in direct mechanical dependence upon the 
torque taken off at the work tool, meaning, independently of the size of 
the cross-section of the exhaust air outlet. The axially displaceable 
component 26 is formed by a sliding sleeve non-rotatably mounted on the 
rotor shaft 6 and, butting surfaces or approach cam tracks 27 in a type of 
spiral toothing which for carrying out of the axial movement of the 
component 26, cooperate with just such counter butting surfaces or 
approach cam tracks 28 of a component 29 mounted axially nondisplaceably 
and with limited rotation on the rotor shaft 6, so as to further transmit 
the rotational movement of the rotor shaft 6 to the work tool 5. When now 
the work tool 5 is more extensively loaded, then the component 29 is 
hereby braked or restrained, whereas the component 26 is continued to be 
driven by the rotor shaft 6. This has as a result that the butting 
surfaces or approach cam tracks 27, 28 slide along each other in a manner 
whereby the component 26 is axially displaced in the sense of a withdrawal 
from the component 29 and hereby controls the valve arrangement 24 for the 
purpose of increasing the introduced air quantity for each unit of time. 
In order to achieve the non-rotatability and concurrently the axial 
displaceability, the component 26 possesses at least one, and preferably 
two diametrically oppositely located axial slits 30 in which there engage 
radial pins 31 fixedly arranged on the rotor shaft 6. The axial slits 30 
extend from one end of the component 26 which is formed as a sliding 
sleeve, whereas at the other end, namely at the end proximate the work 
tool, there are arranged the butting surfaces or approach cam tracks 27. 
The component 26 has additionally associated therewith a spring 32 for 
effecting the assumption of the engaged position of its butting surfaces 
or approach cam tracks 26 with the counter butting surfaces or approach 
cam tracks 28 of the limitedly rotatable component 29. 
The limitedly rotatable, axially undisplaceable component 29 is formed by a 
rotatable sleeve which is supported on the rotor shaft 6 which includes a 
radial slit 33 correlated in its length with the length of the axial 
movement of the axially displaceable component 26, and in which there 
engages a radial pin 34 fixedly mounted on the rotor shaft 6. There now 
occurs an increased loading on the work tool 5, then the components 26 and 
28 rotate relatively to each other until the radial pin 34 comes into 
contact at the end of the radial slit 32. During this displacement the 
butting surfaces or approach cam tracks 27, 28 slide off each other so 
that the component 26 withdraws from the component 29 and thereby the 
valve arrangement 24 controls in the sense of an increase in the 
introduced air quantity per unit of time. 
For the continued transmission of the rotational movement of the rotor 
shaft 6 obtained through the motor 1 to the work tool 5, the component 29 
which is formed by the rotatable sleeve, which is limitedly rotatable with 
respect to the rotor shaft 6 but axially non-slidable, is provided with 
follower elements 35 which, pursuant to FIG. 3, are in engagement with 
follower element 36 on the drive shaft 22 of the handpiece 21. 
As may be ascertained from FIG. 3, on the ends facing each other of the 
sliding sleeve-forming component 26 as well as on the butting surfaces or 
approach cam tracks 27, 28 of the rotatable sleeve forming the component 
29, are presently constructed in the type of the teeth of a spur gear. 
The rotor shaft 6 is provided with a control air channel 36' extending from 
the end remote from the work tool into the axially displaceable component 
26 in its engaged position with the axially non-displaceable component 29 
covered region of the rotor shaft 6, and which includes therein at least 
one radial outlet passageway 35'. Hereby the mouths of the two outlet 
passageways 35' provided pursuant to FIGS. 2 and 3, are in the mentioned 
engaged position coverable by the axially non-slidable component 29 for 
the purpose of venting the control air into the open end, in the 
disengaged position, for the purpose of actuating the vavle arrangement 
24. At the end towards the work tool, the control air passageway 36' is 
closed off by the radial pin 31 which engages into the axial slit 30 in 
the sliding sleeve. 
At the end of the rotor shaft 6 remote from the work tool, the control air 
passageway 36' terminates in a displacement chamber 37 of an axially 
movably supported piston-like valve member 38 which forms the valve 
arrangement 34, which includes a compressed-air passageway 39 constantly 
connected with the compressed-air inlet conduit 3 of the motor 1, and 
which leads to the displacement chamber 18 of the motor 1, which includes 
a branch passageway 40 subjected to compressed air, which at the freeing 
of the mouth of the one or the radial passageways 35' is connected with 
the mouth of the control passageway 36' directed into the displacement 
chamber 37 and, upon the covering of the mouth of the or mouths the radial 
outlet passageways 35' of the referred to displacement chamber 37, for 
effecting an axial movement of the piston-like valve member 38 for 
increasing the compressed air inlet to the displacement chamber 18 of the 
motor 1 for each unit of time. Achieved in this manner, in a particularly 
simple way is an increase in the torque. In order that upon the ending of 
the overloading of the work tool 4 the branch passageway 40 again comes 
into communication with the mouth of the control air passageway 36', a 
return spring 41 is associated with the piston-like valve member 38. 
The compressed-air inlet passageway 39 of the piston-like valve member 38 
is constantly in communication, through the intermediary of a radial inlet 
aperture 42 of a connecting bore 39' having a larger cross-section as the 
last occupied radial inlet aperture 43 of two continuing passageways 45, 
46 leading over the opening 15 or 16 to the displacement chamber 18 of the 
motor 1, and which are arranged in a stationary housing portion 44. 
Hereby, the mentioned inlet aperture 43, pursuant the stroke position of 
the piston-like valve member 38 at release of the mouth of or mouths of 
the radial outlet passageways 35' is adapted to be covered less and upon 
the covering of the mentioned mouths more with the radial outlet aperture 
42 of the compressed-air inlet passageway 39. The exhaust passageways 
which lead from the air exhaust aperture 17 to the exhaust air conduit 19 
are designated with reference numerals 47 and 48. From FIGS. 2 and 3, in 
combination with FIG. 4, there may be ascertained that the piston-like 
valve member 38 is circularly constructed in cross-section and supported 
so as to be limitedly rotatably in the stationary housing portion 44, 
whereby the radial inlet aperture 43 of the continuing passageway 45, 46 
is essentially triangular and includes an axial boundary edge 49 as well 
as a radial boundary edge 50 extending therefrom. The boundary edges 49, 
50 subtend a right angle with each other. The other ends of the boundary 
edges 49, 50 are connected with each other through an inclined extending 
boundary edge 51, like a type of screwline. Met hereby is such an 
arrangement in which the length of the axial boundary edge 49 is 
correlated with the axial path of movement of the piston-like valve member 
38, and the length of the radial boundary edge 50 with the radial path of 
rotation of the piston-like valve member 38, with the task that upon 
release of the mouth of or mouths of the radial outlet passageways 35', in 
the one rotational position of the piston-like valve member 38 
corresponding to a low rated motor speed, only a small covering or 
superposition of the outlet opening 42 is effected with the inlet opening 
43, whereas in another rotational position of the piston-like valve member 
38 corresponding to a higher rated motor speed, the outlet opening 42 is 
fully located within the cross-section of the inlet opening 43 and, 
namely, under contacting of the edge of the outlet opening 42 against the 
axial boundary edge 49 of the inlet opening 43. 
The axial and the rotational movement of the piston-like valve member 38 is 
rendered easier in that a radial passageway 52 branches off from its 
pressure inlet passageway 39, outwardly terminating for subjecting the 
annular gap 53 located between the stationary housing portion 44 
possessing the circularly cylindrical inner surface and the circularly 
cylindrical outer wall of the valve member 38 with compressed air. 
Produced hereby is an air bearing, since an air film will build up in the 
annular gap 53. 
A particularly good correlation with the rated motor is obtained 
particularly when the last-mentioned is relatively low, when the corners 
54 of the essentially triangular inlet aperture 43 are rounded off, and 
the radius of the rounded off portions corresponds to the radius of an 
outlet aperture 42 for the compressed-air inlet passageway 39 of the 
piston-shaped valve member 38, which has a circular cross-section. 
From FIGS. 2 and 3, in combination with FIG. 6, there may be ascertained 
that for a displacement of the piston-like valve member 38 to cause a 
change in the rated motor speed, on the outer wall of the housing 2 there 
is exteriorly rotatably mounted an adjusting ring 55 which is provided 
with a radial follower pin 56 traversing the housing 2 and the stationary 
housing portion 44, which engages in a radial recess 57 provided in the 
piston-like valve member 38 and which has an axial length corresponding to 
the axial stroke movement of the valve member 38. The housing 2 and the 
stationary housing portion 44 each include a cut out 58, 59 for the 
passing through of the follower pin 56, which extend over a radial length 
determining the rotational movement of the piston-like valve member 38. 
For the easy effectuation of a change in the direction of rotation, 
provided in the wall of the essentially circularly cylindrical stationary 
housing portion 44 are two passageways 45, 46 arranged at a distance 
correlated with the right-hand and the left-hand rotation of the rotor, 
presently twice as close to each other, of which in accordance with the 
rotated position of the piston-like valve member 38, one serves 
selectively as a continuing passageway and the other as an exhaust air 
passageway. 
The doubly provided passageways 47 which, independently of the rotational 
position of the piston-like valve member 38 constantly act as exhaust air 
passageways, are provided in addition to the passageways 45, 46 serving 
selectively as continuing passageway and as air exhaust passageway in the 
stationary housing portion 44.