U.S. patent number 3,582,228 [Application Number 04/766,065] was granted by the patent office on 1971-06-01 for apparatus for controlling the rotation of a high-speed rotating spindle.
This patent grant is currently assigned to Toyoda Koki Kabushiki Kaisha. Invention is credited to Tamaki Tomita, Ryuji Wada, Ituo Yokoyama.
United States Patent |
3,582,228 |
Tomita , et al. |
June 1, 1971 |
APPARATUS FOR CONTROLLING THE ROTATION OF A HIGH-SPEED ROTATING
SPINDLE
Abstract
An apparatus for controlling the rotation of a high-speed
rotating spindle supported by gas bearings, the spindle being
maintained in a floating state by a gas film interposed between the
periphery thereof and the peripheries of the bearings and rotated
by a gas turbine coaxially mounted therewith, the bearings and the
turbine being driven by a gas which is supplied from one common
supply source, including means for preventing the spindle from
whirling.
Inventors: |
Tomita; Tamaki (Okazaki,
JA), Wada; Ryuji (Kariya, Aichi Prefecture,
JA), Yokoyama; Ituo (Kariya, Aichi Prefecture,
JA) |
Assignee: |
Toyoda Koki Kabushiki Kaisha
(Kariya, Aichi Prefecture, JA)
|
Family
ID: |
13277414 |
Appl.
No.: |
04/766,065 |
Filed: |
October 9, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Oct 9, 1967 [JA] |
|
|
42-65110 |
|
Current U.S.
Class: |
415/30; 409/231;
415/49; 433/99; 415/904; 433/132 |
Current CPC
Class: |
F01D
25/22 (20130101); Y10T 409/309352 (20150115); Y10S
415/904 (20130101) |
Current International
Class: |
F01D
25/00 (20060101); F01D 25/22 (20060101); F01d
015/06 (); A61c 001/10 () |
Field of
Search: |
;32/3,27 ;308/9
;415/30,49 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Raduazo; Henry F.
Claims
We claim:
1. An apparatus for controlling the rotation of a high-speed
rotating spindle which comprises
a high-speed rotating spindle;
bearing means for supporting said rotating spindle in a floating
condition by a gas film interposed between the periphery of said
bearing means and the periphery of said spindle;
a rotatable gas turbine coaxially fixed to said spindle for
rotating said spindle with a high-speed gas jet running
therethrough;
a common gas source for supplying a pressurized gas directly to
said bearing means and indirectly to said turbine; and
a pressure reducing means connected to said common gas source for
reducing the pressure supplied from said common gas source on the
way to the turbine to prevent unstable movement of said spindle
during rotation thereof.
2. An apparatus for controlling the rotation of a high-speed
rotating spindle as claimed in claim 1, which further comprises
a control means for reducing the pressure to be supplied to said
turbine within the safety range from the unstable movement of said
spindle,
said control means including a spring means and a manually
adjustable screw, said spring means being interposed between said
screw and said pressure reducing means.
3. An apparatus for controlling the rotation of a high-speed
rotating spindle as claimed in claim 1, which further comprises
a rotatable speed detecting means coaxially fixed to said spindle
for discharging a gas according to the spindle speed;
a throttle valve connected to said pressure reducing means for
regulating the gas flow supplied from said pressure reducing means
on the way to said speed detecting means; and
a speed control means for maintaining the spindle speed nearly
constant in response to said speed detecting means in spite of
changes in the loads applied to said spindle.
4. An apparatus for controlling the rotation of a high-speed
rotating spindle as claimed in claim 3, which further comprises
a control means for reducing the pressure to be supplied to the
turbine within the safety range from the unstable movement of said
spindle;
said control means including a spring means and a manually
adjustable screw, said spring means being interposed between said
screw and said pressure reducing means.
5. An apparatus for controlling the rotation of a high-speed
rotating spindle as claimed in claim 1, wherein said pressure
reducing means comprises
a pair of flexible diaphragms;
a throttle rod secured to said diaphragms;
a valve seat provided to form a throttle portion in cooperation
with said throttle rod; and
two chambers separated by said diaphragms, one of said chambers
receiving the pressure supplied from said common gas source and the
other of said chambers receiving the pressure reduced at said
throttle portion.
Whereby the pressure supplied from said common gas source is
controlled and reduced to the pressure to be supplied to said
turbine in accordance with the movement of said diaphragms in
response to the pressure difference between the pressures in said
two chambers to thereby prevent unstable movement of said spindle
during the rotation thereof.
6. An apparatus for controlling the rotation of a high-speed
rotating spindle as claimed in claim 3, wherein said speed control
means comprises
a flexible diaphragm;
a throttle rod secured to said diaphragm;
a valve seat to form a throttle portion in cooperation with said
throttle rod; and
two chambers separated by said diaphragm, one of said chambers
being led to said speed detecting means and the other chamber being
opened to the atmosphere.
Whereby the spindle speed is maintained nearly constant in response
to said speed detecting means in spite of changes in the loads
applied to said spindle.
Description
BACKGROUND OF THE INVENTION
Generally speaking, in the high-speed rotation of a spindle for
supporting tools and the like, it is common practice to provide the
spindle with gas bearings, since such bearings possess extremely
low frictional bearing characteristics and thereby afford an
excellent bearing support for rotation of the spindle. It is also
common practice to employ in high-speed rotation of this spindle
provided with gas bearings a gas turbine drive which can produce a
high revolution of the spindle.
For the purpose of driving both the gas bearings and the gas
turbine it has been common practice to employ separate gas supply
sources for supplying gas to the bearings and for supplying gas to
the turbine. This is due to the fact that the gas pressure for
driving the bearing is quite different from that utilized in
driving the turbine. It is necessary for the bearings to be
supplied with a gas of a relatively high pressure for maintaining
proper and sufficient stiffness of the bearings, while for the
turbine a gas in a relatively large quantity is needed but not one
of a high pressure. Therefore, such prior art practices have
conventionally operated at a disadvantage in that increased costs
of construction, as well as operation and management, have occurred
on account of the employment of separate installations of a gas
source for a supply of high pressurized gas and a gas source for
supply of low pressurized gas of a large volume.
Furthermore, the separate installation of gas supply sources has
created an operational inconvenience in that it has required a
troublesome adjustment of a pressurized gas supplied to the turbine
for prevention of whirling of the rotating spindle.
If the spindle speed has increased high enough, the spindle which
revolves on its axis whirls around at nearly half the speed of the
rotation speed, thereby causing a whirling action of the spindle to
take place, which will be described later. A whirling of the
spindle causes initially an unstable rotation of the spindle and
finally will result in serious failure in the apparatus due to
frictional contact between the spindle and the bearings.
SUMMARY OF THE INVENTION
It is the general object of the present invention to provide an
improved apparatus for controlling the rotation of a high-speed
rotating spindle of the type which employs gas bearings maintaining
the spindle in a floating state and which is driven by a gas
turbine coaxially mounted with the spindle, with both the gas
bearings and the gas turbine being operated by and from one common
gas supply source, whereby the spindle is maintained free from any
unstable movement.
Another object of the present invention is to provide an apparatus
for controlling the rotation of a high-speed rotating spindle
comprising gas bearings and a gas turbine both operated from a
common gas supply source, and including at least one pressure
reducing means for supplying the gas turbine with a gas at a lower
pressure than that supplied to the bearings.
A further object of the present invention is to provide an
apparatus for controlling the rotation of a high-speed rotating
spindle which is simple in construction, easy in operation and
relatively inexpensive to manufacture and maintain.
A still further object of the present invention is to provide an
apparatus for controlling the rotation of a high-speed rotating
spindle which is provided with means for protecting and preventing
the bearing portion from a temperature rise by utilizing gas cooled
by an adiabatic expansion through the gas turbine.
DESCRIPTION OF THE DRAWINGS
The foregoing and other objects of the present invention will
become fully apparent from the following description of some
preferred embodiments of the present invention with reference to
the accompanying drawings, in which:
FIG. 1 is a schematic view of a path of an orbit of the spindle
axis due to a whirling;
FIG. 2 is a diagram illustrating a critical limit to a whirling by
way of showing a relation among pressures supplied to the gas
bearings and the gas turbine and a rotating speed of the
turbine;
FIGS. 3 through 5 inclusive are schematic views of different
embodiments according to the present invention;
FIG. 6 is a cross-sectional view of a materialized structure of the
second schematic embodiment of FIG. 4, the view being taken along
the line VI-VI of FIG. 7;
FIG. 7 is a cross-sectional view taken along the line VII-VII of
FIG. 6;
FIG. 8 is a cross-sectional view taken along the line VIII-VIII of
FIG. 6;
FIG. 9 is a partially cutaway cross-sectional view of a
materialized structure of the third schematic embodiment of FIG. 5;
and
FIG. 10 is a cross-sectional view taken along the line X-X of FIG.
9.
DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, a whirling of the spindle will be
described. When the rotational speed of the spindle becomes so
high, the rotating spindle tends to whirl around an equilibrium
position E along an orbit having an eccentric radius e at nearly
the speed of the axial rotation of the spindle .omega.. This
condition will be hereinafter referred to as a "half-speed
whirling" or simply a "whirling." Once the spindle axial rotation
reaches a speed high enough to cause a half-speed whirling of the
spindle, the rotation of the spindle falls into a critical state
and thereafter in an unstable state. If the rotating speed is
further increased, the amplitude of whirling of the spindle is
increased rapidly until the spindle frictionally touches the
bearings by shearing or breaking down the gas film interposed
therebetween, with the result that it causes a serious failure or
damage to the apparatus, such as bearing seizure. The half-speed
whirling of the spindle occurs when the rotating speed of the
spindle exceeds a certain critical speed as the onset-speed or the
threshold speed of the half-speed whirling of the spindle. It was
found that the onset-speed of the spindle largely depends upon the
stiffness of the bearings, and accordingly that it increases or
rises in accordance with an increased stiffness of the
bearings.
A relation between stiffness of the bearings and the rotation speed
of the turbine is shown in FIG. 2 by way of illustration of the
relation between a gas pressure supplied to the bearings and a gas
pressure supplied to the turbine. In FIG. 2, a curve A indicates
the critical state of a half-speed whirling as a function of
dimensionless numbers of the pressure supplied to the bearings and
the number of the rotation of the turbine. The stable rotation of
the spindle is generated below the curve A. The spindle rotation is
extremely unstable above the curve A due to its half-speed
whirling. The curve B indicates the spindle speed of rotation as a
function of dimensionless numbers of the pressure supplied to the
turbine.
The maximum pressure supplied to the turbine to the pressure
supplied to the bearings is easily read from the diagram of FIG. 2.
For instance, when P.sub.1 /Po as a factor of the pressure supplied
to the bearings is set at 0.7, P.sub.2 or P.sub.3 /Pe as a factor
of the pressure supplied to the turbine reaches about 0.6 at the
maximum, and N/No as a factor of the turbine rotation speed falls
about 0.9 at the maximum. Pe, Po and No respectively represent
constants as follows:
Pe: constant for the pressure supplied to the turbine P.sub.2 or
P.sub.3
Po: constant for the pressure supplied to the bearings P.sub.1
No: constant for the spindle speed of rotation N
According to the prevent invention, it is most likely to apply the
following actual values respectively to said constants as a
preferred example:
Pe: 50 p.s.i.
Po: 100 p.s.i.
No: 50,000 r.p.m.
It is an essential requirement to supply the turbine with a gas
pressure lower than the threshold pressure of the half-speed
whirling of the spindle, or otherwise, the apparatus would likely
be subjected to heavy failure or damage.
Referring now to FIG. 3, the first embodiment according to the
present invention is schematically shown. In FIG. 3, the portion
enclosed by a phantom line 10 includes the bearing and turbine
means. A rotating spindle 1, which has a gas turbine 4 coaxially
mounted at one end of the spindle, is supported by suitable
gas-lubricated radial bearings 2 and a thrust bearing 3. A common
gas supply source 20 supplies the bearings 2 and 3, as well as the
turbine 4, with a pressurized gas, either directly or indirectly
via suitable conduits 21 or 27. The pressurized gas P.sub.1 is
supplied to the bearings 2 and 3 directly from the common gas
source 20, while the gas turbine 4 is connected with the common gas
source 20 via a pressure reducing valve 30 which serves to reduce
the pressure supplied from the gas source 20 low enough to prevent
the spindle 1 from reaching the half-speed whirling stage mentioned
above. The pressure reducing ratio between the primarily supplied
pressure P.sub.1 and the secondarily reduced pressure P.sub.2, that
is, the pressure supplied to the turbine 4, is kept constantly
lower than that of the critical state to thereby prevent the
whirling of the spindle, this being accomplished by means of the
pressure reducing valve 30 being set at a ratio of m:1 as described
in detail hereafter.
The pressure reducing ratio depends upon an effective diameter
ratio between a smaller-diameter diaphragm 31 and a larger-diameter
diaphragm 32, where the supply pressure P.sub.1 is applied to the
smaller-diameter diaphragm 31 via the radial conduit 27 and an
axial conduit 51 and the reduced pressure P.sub.2 is applied to the
larger-diameter diaphragm 32 via a conduit 53. When the ratio
between the supply pressure P.sub.1 and the reduced pressure
P.sub.2 is other than the predetermined ratio, m:1, an equilibrium
state of a throttle rod 33 fails. Thereupon the position of the
throttle rod 33 is moved to change the throttling capacity at a
throttle portion or throat 34 accordingly, so that the
predetermined ratio m:1, is restored and maintained. That is, the
pressure reducing ratio predetermined at m:1 is so maintained that
the turbine 4 is supplied with the reduced pressure within a safety
range in relation to the pressure supplied to the bearings 2 and 3
thus avoiding the half-speed whirling of the spindle even if the
supply pressure P.sub.1 is varied. According to the present
invention, "m" of the pressure reducing ratio is preferred to be
settled or selected at more than 2.
Referring now to FIG. 4, the second embodiment according to the
present invention is schematically illustrated. This embodiment
achieves a control of the turbine speed as well as the prevention
of the whirling. In this modification the supply pressure P.sub.1
from the gas pressure source 20 is controlled according to the same
principle as in the first embodiment of FIG. 3 so as to be reduced
to the pressure P.sub.2 supplied to the turbine 4 and which is made
variable within the safety range from the half-speed whirling. The
means for controlling the pressure to the turbine 4 comprises a
compression spring 35 and an adjusting screw 57 which may be turned
by knob 59 and which adjustably compresses the spring 35. The
spring 35 biases the throttle rod 33, fixed to the diaphragms 31
and 32, towards the left, as viewed in the drawings. An equilibrium
position of the throttle rod 33 is shifted by manually adjusting
the biasing force of the compression spring 35 by means of the
screw 57, so that a throttling capacity at the throttle or throat
portion 34 is so controlled to change within the safety range.
Thus, the delivery pressure P.sub.2 to the turbine 4 is changed
within the safety range from the whirling. As the turbine speed is
changeable arbitrarily within the stable range of the turbine
rotation, the most favorable condition of rotation is obtained
which is variable according to the kind of tool attached to the end
of the spindle and the conditions present.
The third embodiment according to the present invention is
schematically illustrated in FIG. 5. The general purpose of the
third embodiment is to control the turbine speed of rotation to
prevent the spindle from whirling. A more particular purpose is to
automatically keep the spindle speed of rotation nearly constant at
a predetermined ratio of m:1, even if there are some changes of the
load applied to the spindle 1. The pressure reducing valve is the
same as shown in FIG. 3. The gas of the reduced pressure P.sub.2
flows into a speed control valve 40 via a conduit 70 where it is
further reduced in pressure before introduction into the turbine 4.
To explain this in detail, the gas of the reduced pressure P.sub.2
is introduced into a valve chamber 41 via line 70 and a throttle
valve 50 which controls flow of the gas running therein. The
pressure in the valve chamber 41 is regulated by the speed control
valve 40 functioning to maintain constant the pressure responding
to the volume of the gas flowing through the throttle valve 50 and
the volume of the gas leaving or discharged from a speed detecting
turbine 7. Assuming that the spindle speed of rotation is
decelerated due to the load applied to the spindle 1, the amount of
discharged gas leaving the speed detecting turbine 7 will decrease,
whereby the pressure in the valve chamber 41 will rise. With this
increase in pressure in chamber 41, a throttle rod 45, secured to a
diaphragm 44, will move to the right increasing the valve opening
to thereby increase the pressure P.sub.3 supplied to the turbine 4
and to thereby restore the spindle speed of rotation. As above
mentioned, it is the main feature of this third embodiment to
maintain the spindle rotation at nearly a predetermined constant
speed. The turbine speed of rotation is changeable and set manually
by controlling an opening degree of the throttle valve 50, which
will shift the equilibrium position of the throttle rod 45. The
pressure to be supplied to the turbine 4 is thus so controlled that
the turbine speed of rotation, which is determined and selected by
adjustment of the throttle valve 50, is maintained.
FIG. 6 through FIG. 10 inclusive indicate actual structures of some
of the foregoing embodiments. The materialized structure of the
first embodiment is not explained here to avoid a double
explanation in view of the fact that the first embodiment shown in
FIG. 3 can be modified to the second embodiment shown in FIG. 4 if
the former is combined with a control means comprising an adjust
screw 57 and a knob 59, etc. as additional means.
The materialized structure of the second embodiment shown
schematically in FIG. 4 is illustrated in FIGS. 6, 7 and 8. Radial
bearings 2, radially spaced around the rotating spindle 1, and a
thrust bearing 3, axially spaced around the peripheral sides of an
enlargement 1a protruding radially from the rotating spindle 1, are
integrally provided in an internal bore 9 of a spindle housing body
8. A plurality of radial apertures 12 and axial apertures 13 are
respectively provided through the bearings 2 and 3 extending from
the bearing surfaces and are connected to a supply conduit 21 via
annular grooves 14 and radial conduits 15. The supply conduit 21
runs parallel to the spindle 1 and extends longitudinally along the
spindle housing body 8 and a valve housing 71. The gas from the
supply conduit 21 flows into a clearance between the peripheries of
the bearings 2 and the periphery of the spindle 1 for supporting
the spindle 1 in a floating condition and thence through discharge
chamber 23 which leads to the atmosphere, via radial and axial
conduits 22, exteriorly of the spindle housing body 8.
The turbine 4 is coaxially fixed to an end of the spindle 1 as
previously stated. The conduits 22 also receive the gas leaving the
turbine 4 which gas by expansion has been cooled to a lower
temperature than the room temperature by 10 and more degrees
Centigrade, thereby preventing the bearings from being overheated.
Discharge conduits 22 extend parallel to the spindle 1 and are
located circumferentially equal distance from each other so as to
eliminate any local thermal deformations of the spindle housing
body 8 and the bearings and to thus equalize the temperature
distribution around the bearings.
A nozzle block 5a is slidably mounted in a bore 6 formed in a
casing 6a and is provided with a plurality of axial nozzles 5. One
side of the nozzle block 5a faces toward one side of the turbine 4
with a clearance that is changeable by a capscrew 25 and a
compression spring 26 which eliminates the backlash of the capscrew
25. One end of the capscrew 25 is secured to a plate 24 mounted
within the casing 6a, while the opposite end threadedly engages
with the nozzle block 5a. The compression spring 26 normally biases
the nozzle block 5a toward the left, with one end of the
compression spring 26 bearing against the other side of the nozzle
block 5a, while the opposite end of the spring 26 abuts a surface
of the plate 24. The highest efficiency of the turbine 4 may be
obtained by adjusting a clearance between the turbine 4 and the
nozzle block 5a. The other side (left side) of the turbine 4 is
open to the discharge chamber 23 which is in turn connected to the
conduits 22 as mentioned above. The turbine 4 is rotated at high
speed when the gas jet projected from the turbine nozzles 5 flows
axially along the turbine blades.
While the turbine depicted in FIG. 6 is shown as an axial flow
turbine, it will be appreciated that any other type of turbine may
be applied.
A hollow valve housing 71 aligned with the spindle body 8 is
coaxially fixed to one end of the spindle body 8 by means of
capscrews (not shown). A pressure reducing valve 30 is contained
within an outer sleeve 37 mounted within the inner surface 72 of
the valve housing 71. As mentioned above the pressure reducing
valve 30 is provided with a smaller diaphragm 31 and a larger
diaphragm 32 which are of different effective diameters. The
smaller-diameter diaphragm 31 is fixed or held at its rim between a
ring 36 and an inner sleeve 73 which are mounted within and on the
outer sleeve 37. The larger-diameter diaphragm is fixed or held at
its rim by being clamped between the ring 36 and the outer sleeve
37. A throttle rod 33 slidably supported through an opening in the
inner sleeve 73 is fixed to the diaphragms 31 and 32 by means of
nuts 74 and 75 interposing therebetween a spacer collar 76 and a
washer 77. A conical end 33a of the throttle rod 33 forms a
variable throttle or throat portion 34 in cooperation with the
valve seat 38. The valve seat 38 presenting its throat 34 in
alignment with the throttle rod 33, is fixed to the inner sleeve
73. An inlet throttle chamber 78 is connected to the supply conduit
21 via a radial conduit 27. An outlet throttle chamber 39,
connected to the inlet throttle chamber 78 through the throttle
portion 34, is in turn connected to the nozzles 5 via the holes 24a
perforated in the plate 24. A smaller chamber 52 formed by and
between the diaphragm 31 and the inner sleeve 73 is connected to
the inlet throttle chamber 78 via a passageway 51 extending axially
through the inner sleeve 73 for introducing the supply pressure
P.sub.1. A larger chamber 54 formed adjacent the larger-diameter
diaphragm 32 is connected to the outlet throttle chamber 39 via a
conduit 53 for introducing the reduced pressure P.sub.2. The
throttle rod 33 is moved in response to the difference in the two
pressures P.sub.1 and P.sub.2 applied respectively to the
diaphragms 31 and 32 in order to keep the pressure reducing ratio
constant. A compression spring 35 provided in the chamber 54
normally urges both the diaphragms 31 and 32 to the left via the
collar 76. One end of the spring 35 bears against the washer 77,
while the opposite end of the spring 35 abuts a washer 55 which is
threadedly engaged with an adjustment screw 57 and retained therein
by a pin 58 against rotation. The adjustment screw 57 is rotatably
supported in the valve housing 71 and has one end protruding from
the valve housing. A knob 59 is secured on the protruded end of the
adjustment screw 57 by a pin 78 so that the same can be manually
turned to control the compression force of the spring 35.
The gas with its pressure reduced from the supply pressure P.sub.1
at the variable throttle portion 34, is introduced to the turbine
nozzles 5 through the orifices or holes 24a in the plate 24, and
thence flows axially along the blades of the turbine 4. After
passing through the turbine the gas flows out into the chamber 23
which is connected to the discharge conduits 22, and it is thus
adiabatically expanded, thus lowering its temperature to lower than
the room temperature by 10.degree. C. and more. The gas thus cooled
prevents the bearing surfaces from undue temperature rise. The
thrust bearing 3, which is most likely to be subject to heat, is
prevented from temperature rises by the annular chamber 23 being
positioned adjacent thereto. The gas flowing through the discharge
conduits 22, equally spaced from each other circumferentially along
the radial bearings 2, can cool equally all the radial bearing
peripheries, as well as the whole apparatus, to avoid any local
thermal deformation.
The pressure reducing ratio at the valve 30 is variable in response
to the compression of the spring 35 which is controllable through
the screw 57 by a manual adjustment of the knob 59. The smallest
compression of the spring 35 results in the pressure reducing ratio
of the effective-diameter ratio between the diaphragms in which the
highest pressure within the safety range is supplied to the
turbine. The compression of the spring 35 is so determined that the
reduced pressure P.sub.2 supplied to the turbine does not exceed
the threshold pressure to cause the half-speed whirling.
The equilibrium position of the throttle rod 33 is shifted in
proportion to the compression force of the spring, and thereby the
spindle speed is changeable arbitrarily within the safety range
from the half-speed whirling by means of the knob 59.
Reading the diagram of FIG. 2, the critical pressure reducing ratio
between the supply pressure P.sub.1 and the reduced pressure
P.sub.2 may be decided according to the curve A. However, for the
sake of safety the actual ratio is chosen below the curve A. For
example, if the ratio is selected below the phantom line C, the
spindle will never be rotated in an unstable state. The reducing
ratio of the pressure reducing valve 30 is constant and keeps the
reduced pressure P.sub.2 from exceeding the critical pressure in
spite of any changes in the supply pressure. Therefore, an operator
can change the spindle speed of rotation with no trouble merely by
turning the knob 59 as long as the spindle is currently free from
the half-speed whirling.
Referring now to FIGS. 9 and 10, an actual adaptation and structure
of the third embodiment schematically shown in FIG. 5 is
illustrated. The structure of the bearing portion, the turbine and
the pressure reducing valve 30, without the control means for
changing the compression force of the spring 35, are the same as
those in FIG. 6.
A speed control valve 40 is provided in series with the gas flow
through conduit 70 of the reduced pressure P.sub.2 coming for the
pressure reducing valve 30, to automatically control the reduced
pressure to be delivered to the turbine 4 for the purpose of
maintaining the spindle speed of rotation almost constant in spite
of differences in the loads applied to the spindle 1. The speed
control valve 40 is located between the pressure reducing valve 30
and the plate 24 contained in the valve housing 71. An outer sleeve
43, closed at one end, the right end as viewed in the drawing, is
mounted within the inner surface of the valve casing 71, and an
inner sleeve 79 is mounted within the outer sleeve 43. A diaphragm
44, fixed between abutting surfaces of the outer sleeve 43 and the
inner sleeve 79, separates a space formed by the sleeves into two
chambers 41 and 42. A throttle rod 45 slidably supported through an
opening in the inner sleeve 79 is fixed to the diaphragm 44 by
means of nuts 80 and 81 interposing therebetween collars 82 and 83.
A conical end 45a of the throttle rod 45 and a valve seat 47
mounted on the inner sleeve 79 form a throttle or throat portion
47a in a chamber 46. The chamber 46 is connected with the outlet
throttle chamber 39 via a conduit 70. The gas under reduced
pressure P.sub.2 introduced from the pressure reducing valve 30
through the conduit 70 is further reduced in pressure at the
throttle portion 47a on its way to the axial-flow turbine 4. The
separated valve chamber 42 is opened to the atmosphere via an
aperture 48. A compression spring 49 in the chamber 42 normally
biases the throttle rod 45 toward the left. One end of the spring
49 bears against the end of the outer sleeve 43, while the opposite
end of the spring 49 abuts the collar 83.
A throttle valve 50 includes a valve seat in a radial conduit
opposite and leading to the chamber 46, the valve seat cooperating
with a throttle rod 50a adjustably threaded through the valve
housing wall 71. The other valve chamber 41 of speed control valve
40 is connected with the chamber 46 through the radial conduit and
the throttle valve 50 and is also connected to a speed detecting
turbine 7, coaxially fixed to the spindle 1, through the axial
conduit 60. There is formed a small clearance between the internal
periphery 61 of the sleeve 6a and the outer surface of turbine 7. A
plurality of convex depressions 17 are provided on the periphery of
the turbine 7 at an equal distance from each other. A pair of
nozzles 18 and 18' oppositely extending from the periphery 61 of
the inner sleeve 6a are connected to the chamber 41 via an annular
groove 62 and the conduit 60 to detect the spindle speed of
rotation. A pair of pockets 19 and 19' opening to the chamber 23
are provided on the periphery 61 of the inner sleeve 6a. The convex
portions 17 on the turbine 7 carry the gas poured from the nozzle
18 or 18' to the pockets 19 and 19' in proportion to the turbine
speed of rotation. The gas led to the speed detecting turbine 7 is
limited by the throttle valve 50, so that the pressure in the valve
chamber 41 is regulated according to the turbine speed of
rotation.
Assuming that the spindle speed of rotation is decelerated by the
loads applied to the spindle 1, the gas quantity flowing out of the
speed detecting turbine 7 is decreased accordingly and thereby the
pressure in the chamber 41 is increased resulting in moving of the
throttle rod 45 to the right to open the throttle portion 47a to a
greater degree and consequently increasing the spindle speed. When
the spindle speed is accelerated, the gas quantity flowing out from
the turbine 7 is increased and thereby the pressure in the chamber
41 is decreased, resulting in the moving of the throttle rod 45
towards the left, toward closed position, thus the spindle speed of
rotation is decelerated. Thus, the pressure of the gas supplied to
the turbine 4 is regulated automatically to maintain the spindle
speed nearly constant. The speed control valve 40 cannot make the
pressure to be introduced to the turbine 4 any higher than the
reduced pressure P.sub.2 even though the throttle rod 45 moved to
the right the maximum distance, so that the function of the
pressure reducing valve 30 to prevent the spindle from the
half-speed whirling is still maintained and protected. The valve 40
controls the pressure supplied to the turbine 4 to maintain the
spindle speed nearly constant without regard to the loads applied
to the spindle 1. The throttle valve 50 permits manual change of a
predetermined spindle speed by shifting an equilibrium position of
the throttle rod 45 due to a pressure change within the valve
chamber 41 controlled by the throttle valve 50.
As above mentioned, it is in the first embodiment that the pressure
reducing ratio between the pressures to the bearings P.sub.1 and to
the turbine P.sub.2 is maintained constant in order to prevent the
spindle from the half-speed whirling. It is in the second
embodiment that the pressure reducing ratio between the pressures
P.sub.1 and P.sub.2 is controlled in order to prevent the spindle
from the half-speed whirling and the pressure supplied to the
turbine is changeable within the safety range from the half-speed
whirling by manually turning the knob 59. It is in the third
embodiment that the pressure supplied to the pressure reducing
valve 30 is reduced with a constant ratio to prevent the half-speed
whirling and the gas of the reduced pressure P.sub.2 is supplied to
the turbine 4 through the speed control valve 40 in order to keep
the spindle speed nearly constant in spite of the changes of the
loads applied to the spindle 1. The reduced pressure P.sub.2 from
the supply pressure P.sub.1 is controlled automatically in
accordance with the spindle speed within the range "0" to the
maximum of the reduced pressure.
It is also possible to further modify the third embodiment with a
means like the screw and the knob employed in the second embodiment
to manually control the reduced pressure P.sub.2 to be changeable
within the safety range from the half-speed whirling.
While the foregoing description is concerned with the preferred
embodiments of the present invention, it will be evident to those
skilled in the art that various changes and modifications may be
made therein without thereby departing from the basic principle of
the invention, and the appended claims are intended to cover all
such changes and modifications as fall within the spirit and scope
of the invention.
* * * * *