Variable capacity turbine

Disclosed is a turbine comprising a turbine wheel, a turbine scroll passage defined in a turbine casing around the turbine wheel for introduction of gas to the turbine wheel, and an axial central passage defined in the turbine casing for ejection of gas from the turbine wheel, wherein: a plurality of variable nozzles are arranged outside of a throat section having a locally minimum cross section which is defined in the turbine casing around the turbine wheel. The variable nozzles may be defined by fixed vanes and moveable vanes which cooperate with each other in such a manner that each of the moveable vanes and the corresponding fixed vane define a substantially smooth and continuous airfoil. The moveable vanes may be pivotally supported by a back plate of the casing while the fixed vanes may be integrally provided with a fixed vane member having a disk portion which defines a surface opposing the inner surface of the back plate. The moveable vanes may rotate along and between these mutually opposing surfaces for varying the cross section of the nozzles defined between the fixed vanes and the moveable vanes.

TECHNICAL FIELD 
The present invention relates to a variable capacity turbine and in 
particular to a variable capacity turbine suitable for use in a 
turbosupercharger which is simple in structure and can yet maintain a high 
level of efficiency even when the velocity of the fluid supplied to the 
turbine is low. 
BACKGROUND OF THE INVENTION 
In the radial turbine which is typically employed as an exhaust gas turbine 
of a turbosupercharger, it is often desirable to be able to supercharge 
the engine even at a relatively low engine speed and this can be achieved 
by increasing the velocity of the exhaust gas entering the turbine by 
restricting the cross section of the passage leading to the turbine wheel. 
However, when the passage is restricted, the inlet pressure of the turbine 
or the back pressure of the engine exhaust system rises and the efficiency 
of the engine drops. 
Therefore, if a plurality of moveable vanes are arranged in a throat 
located adjacent the outer circumference of a turbine wheel in a circle so 
that the area of the nozzles defined between the moveable vanes may be 
varied by rotating the moveable vanes over a certain angle as described in 
Japanese Patent Publication No. 38-7653, it is possible to ensure 
supercharging of the engine in a low speed range of the engine and, at the 
same time, to keep the back pressure of the engine exhaust system to a low 
level in a medium to high speed range of the engine. 
However, in this structure, since the vanes are placed in the region where 
the velocity of the fluid flow is relatively high, the resistance loss of 
the fluid tends to be great and, therefore, the efficiency of the turbine 
tends to drop. And, since the nozzles are defined between neighboring 
moveable vanes, a slight error in the angle of the vanes causes a 
significant change in the opening area of the nozzles particularly when 
the opening area of the nozzles is small and, therefore, a difficulty 
arises in ensuring a control precision. When this turbine is applied as an 
exhaust turbine in a turbosupercharger, since these vanes are exposed to 
an exhaust gas flow of high temperature, it is difficult to adjust these 
vanes with a high level of reliability. 
Furthermore, since the vanes defining the variable nozzles are arranged to 
rotate along and between the inner surface of the turbine casing and the 
inner surface of the back plate which closes the turbine wheel bearing end 
of the casing and the thermal expansion of the turbine casing having a 
complicated shape is highly uneven, the gap control of the variable 
nozzles particularly in a high temperature environment could be a serious 
problem. 
As disclosed in Japanese Patent Laid Open Publication 53-136113, it is 
previously known to change the cross sectional area of a scroll passage of 
a turbine casing by providing a moveable flap which defines a part of the 
wall of the scroll passage. In this variable nozzle structure, the 
velocity of fluid flowing into the turbine wheel can be adjusted without 
involving much resistance loss with a simple structure, but the range of 
variation is not as wide as desired and particularly when the flap opening 
is great the flow heading toward the turbine wheel tends to be disturbed 
with the result that the distribution of the fluid velocity tends to be 
uneven and, therefore, the efficiency of the turbine drops. 
BRIEF SUMMARY OF THE INVENTION 
In view of such problems of the prior art, a primary object of the present 
invention is to provide a variable capacity turbine which can operate even 
when the flow rate of the fluid entering the turbine is small and, yet, 
allows the passage of the fluid flow without involving a significant 
pressure drop when the flow rate of the fluid entering the turbine has 
increased. 
A second object of the present invention is to provide a variable capacity 
turbine which allows a wide range of variation without increasing the 
resistance loss of the fluid. 
A third object of the present invention is to provide a variable capacity 
turbine which is capable of controlling the entry velocity of fluid into 
the turbine wheel with a high level of reliability even in a high 
temperature environment. 
A fourth object of the present invention is to provide a variable capacity 
turbine in which the clearance of the side edges of the moveable vanes is 
minimized when the opening of the variable nozzles is small so as to 
improved the efficiency of the turbine. 
A fifth object of the present invention is to provide a variable capacity 
turbine which is free from the mechanical seizure of the moving parts of 
the turbine. 
These and other object of the present invention can be accomplished by 
providing a turbine comprising a turbine wheel, a turbine scroll passage 
defined in a turbine casing around the turbine wheel for introduction of 
gas to the turbine wheel, and an axial central passage defined in the 
turbine casing for ejection of gas from the turbine wheel, wherein: a 
plurality of variable nozzles are arranged outside of a throat section 
having a locally minimum cross section which is defined in the turbine 
casing around the turbine wheel. The variable nozzles may be defined by 
fixed vanes and moveable vanes. Preferably, the fixed vanes are comprised 
of arcuate vanes arranged along a circle which is concentric to the 
turbine wheel and the moveable vanes are adapted to rotate along a plane 
which is perpendicular to the axial line of the turbine. 
Thus, since the variable nozzles are provided in the region where the cross 
sectional area of the flow passage is relatively great the resistance loss 
of the fluid can be minimized, and since the variable nozzle structure is 
disposed in an annular arrangement around the outer circumference of the 
turbine wheel the velocity distribution of the flow entering the turbine 
wheel can be made uniform even when the nozzle opening is great. 
According to a certain aspect of the present invention, the moveable vanes 
are each provided with a center of rotation at its base end which is 
adjacent to one of the fixed vanes and are adapted to rotate between a 
most closed position which is substantially aligned with the circle and a 
most open position which is inclined inwardly with respect to the circle. 
Preferably each of the fixed vanes and the corresponding moveable vane 
define a substantially continuous and smooth airfoil. 
According to another aspect of the present invention, the variable capacity 
turbine of the present invention may comprise a fixed vane member having a 
disk portion which defines a surface opposing an inner surface of a back 
plate which covers an axial end of the turbine casing remote from the 
central axial passage and the fixed vanes arranged at an equal interval 
along a peripheral portion of the disk portion radially outside of the 
outer periphery of the turbine wheel and extend axially towards the back 
plate; moveable vane members having the moveable vanes and pivot means for 
supporting the moveable vanes in a rotatable manner along and between the 
opposing surfaces of the disk portion and the back plate; a fastener for 
connecting an axial free ends of the fixed vanes to the back plate. 
Thus, the variable nozzle are defined between the internal surface of the 
back plate, the opposing surface of disk portion of the fixed vane member 
which is a separate member from the turbine casing, the fixed vanes and 
the moveable vane. Since the back plate and the fixed vane member are 
rigidly connected to each other by the free ends of the fixed vane and the 
fixed vane member may have a relatively uniform shape, favorable 
management and control of the gaps of the moveable vanes is possible even 
when gas of a high temperature is introduced into the turbine and thermal 
deformation of various parts are caused. 
According to yet another aspect of the present invention, the moveable 
vanes are pivotally supported by the back plate. Preferably, the gap 
defined by the back plate and the disk portion for receiving one of the 
moveable vane is flared from an outer circumferential portion thereof to 
an inner circumferential portion thereof. This feature is helpful because 
the clearance between the side edges of the movable vane and the back 
plate and/or the disk portion of the fixed vane member is minimized when 
the opening of the variable nozzles is small so as to maximize the turbine 
efficiency, and the clearance of the moveable vanes is maximized when the 
opening of the variable nozzles is fully open so as to eliminate the 
possibility of mechanical seizure of the moveable vanes. 
According to a certain structurally advantageous feature of the present 
invention, the disk portion of the fixed vane member is provided with a 
central tubular portion which is adapted to be connected to an internal 
end of the axial passage in a substantially air tight and floating manner. 
According to yet another aspect of the present invention, the minimum 
opening angle of the moveable vanes is determined by the side edges of the 
moveable vanes contacting complementary shoulders formed in at least 
either one of the back plate and the disk portion of the fixed vane 
member. This feature ensures a precise positioning of the moveable vanes 
and minimizes the leakage of the gas from the side edges of the moveable 
vanes when the opening area of the variable nozzles is at its minimum. 
According to yet another aspect of the present invention, an overlap along 
the circumferential direction is provided between the leading edge of each 
of the fixed vanes and the trailing edge of the corresponding moveable 
vane, the ratio of this overlap to the width of the moveable vane being 
from 20 to 60%, more preferably from 20 to 30%.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now an embodiment of the present invention is described in the following 
with reference to the appended drawings. 
FIGS. 1 and 2 show a turbosupercharger for an engine to which the variable 
capacity turbine of the present invention is applied. This 
turbosupercharger comprises an overall casing which consists of a 
compressor casing 1 which defines a scroll passage of a compressor unit, a 
back plate 2 which covers the back face of the compressor casing 1, a 
lubrication unit casing 3 which incorporates a structure for lubricating 
the main shaft of the turbosupercharger, a turbine casing 4 which defines 
the scroll passage of the turbine unit, and another back plate 23 which 
covers the back face of the turbine casing 4. 
Inside the compressor casing 1 are defined a scroll passage 5 and an axial 
passage 6. A compressor wheel 7 is provided in a central part of the 
scroll passage 5 adjacent the internal end of the axial passage 6. This 
compressor wheel 7 is mounted to an end of a main shaft 8 of the 
turbosupercharger, in such manner as described hereinafter, which is 
supported in a freely rotatable manner in the center of the lubrication 
unit casing 3. In this compressor unit, the scroll passage 5 serves as an 
outlet passage for intake air while the axial passage 6 serves as an inlet 
passage for intake air as indicated by the arrows in FIG. 1. 
The compressor casing 1 and the back plate 2 are integrally attached to 
each other by means of bolts 10 which are threaded with the outer 
circumferential portion of the compressor casing 1 by way of a ring member 
9. The central part of the back plate 2 is provided with a depression 
which fixedly receives the outer circumferential surface of the 
lubrication unit casing 3. 
The main shaft 8 is supported as mentioned earlier in a pair of bearing 
holes 11 and 12 defined in the lubrication unit casing 3 by way of radial 
bearing metals 13. A thrust bearing metal 14 is placed between the back 
plate 2 and the lubrication unit casing 3, and the support of the main 
shaft 8 in the thrust direction and the mounting of the compressor wheel 7 
on the main shaft 8 are accomplished by fitting a washer 15, a collar 15a 
which is received in a central hole of the thrust bearing metal 14, a 
bushing 16 and the compressor wheel 7 onto the main shaft in that order 
with the washer 15 engaging an annular shoulder formed in the main shaft 8 
and by threading a nut 18 with a threaded portion 17 formed on the 
compressor end of the main shaft 8. The collar 15a serves as a spacer for 
controlling the interposing pressure acting on the thrust bearing metal 
14. 
When threading the nut 18 with the threaded portion 17, by holding a 
hexagonal cross section portion 19 provided in the free end of the 
threaded portion 17 with an appropriate hand tool, the main shaft 8 is 
prevented from turning and no excessive twisting force will be applied to 
the intermediate portion of the main shaft 8. 
The turbine casing 4 defines therein a scroll passage 21, an inlet opening 
21a of the scroll passage 21 which opens in a tangential direction, an 
outlet passage 22 extending in an axial direction and an outlet opening 
22a for this outlet passage 22. And the direction of the flow of exhaust 
gas in these passages are indicated by the arrows in FIG. 1. 
The back plate 23 is interposed between the turbine casing 4 and the 
lubrication unit casing 3 at its flange 23a which extends radially from 
the outer circumferential portion of the back plate 23. The connection 
between the turbine casing 4 and the lubrication unit casing 3 is 
accomplished by threading nuts 26 with stud bolts 24 provided in the 
turbine casing 4 by way of a ring member 25 in such a manner that the 
outer circumferential portion of the lubrication unit casing 3 and the 
flange 23a of the back plate 23 are held between the outer circumferential 
portion of the turbine casing 3 and the ring member 25. 
A fixed vane member 27 for dividing the scroll passage 21 into an outer 
circumferential passage 21b and an inlet passage 21c is provided in a 
central portion of the scroll passage 21. This fixed vane member 27 
comprises a tubular portion 28a provided in a central portion thereof, a 
disk portion 28b extending radially from the outer circumferential portion 
of an axially intermediate portion of the tubular portion 28a, and fixed 
vanes 29 which extend axially from the outer circumferential portion of 
the disk portion 28b towards the lubrication unit casing 3, and a turbine 
wheel 30 integrally mounted on the other end of the main shaft 8 is 
received in the tubular portion 28a. The tubular portion 28a is further 
fitted into an internal end portion of the outlet passage 22 by way of a 
pair of metallic seal rings 31 and an axial end portion of the fixed vane 
29 is connected to the back plate 23 with bolts 32. The internal end of 
the tubular portion 28a defines a throat or a portion of a locally minimum 
cross section in cooperation with the back plate 23. 
As best shown in FIG. 2, the outer circumferential portion of the fixed 
vane member 27 is provided with four of the fixed vanes 29 which surround 
the turbine wheel 30 in a concentric manner. These fixed vanes 29 are 
arcuate in shape and are arranged at an equal interval along a 
circumferential direction. The gaps between the fixed vanes 29 can be 
opened and closed with moveable vanes 34 which are each rotatably 
supported by a pin 33 which is fixedly attached to the corresponding 
moveable vane 34 and is received in a hole provided in the back plate 23. 
These moveable vanes 34 which are arcuate in shape by having a same 
curvature as that of the fixed vanes 29 are located along a same circle as 
the fixed vanes 29. And these moveable vanes 34 are pivoted at their 
portions adjacent the circumferential ends of the corresponding fixed 
vanes 29 in such a manner that they can only be moved into the interior of 
the circle. 
Thus, the fixed vanes 29 and the corresponding moveable vanes 34 define the 
leading edges and the trailing edges of four smooth airfoil vanes, 
respectively, for the fluid flowing through the outer circumferential 
passage 21b of the scroll passage 21. And, when the moveable vanes 34 are 
in their fully closed positions, the trailing edges of the airfoils or the 
free ends of the moveable vanes 34 slightly overlap the leading edges of 
the adjacent air foils or the circumferential ends of the fixed vanes 29 
remote from the pins 33 defining a certain gap g.sub.min therebetween. The 
external ends of the pins 33 supporting the moveable vanes 34 are 
connected to an actuator which is not shown in the drawings by way of an 
appropriate linkage mechanism 35 so that the opening angles of the 
moveable vanes 34 can be adjusted according to a certain control signal. 
Since the linkage mechanism 35 itself is not directly related to the 
present invention, its description is omitted here. An example of 
mechanism for actuating the moveable vanes 34 is described in greater 
detail in the copending patent application which was filed on even date. 
A shield plate 36 is interposed between the back plate 23 of the turbine 
unit and the lubrication unit casing 3 and extends towards the rear face 
of the turbine wheel 30 so a to prevent the heat from the exhaust gas 
flowing through the exhaust gas turbine unit from being transmitted to the 
interior of the lubrication unit casing 3. Further, in order to prevent 
the exhaust gas of the turbine unit from leaking into the interior of the 
lubrication unit casing 3 a plurality of annular grooves 38 serving as a 
labyrinth seal are formed around the portion of the main shaft 8 which is 
passed through a central hole 37 of the lubrication unit casing 3. 
Now the lubrication system of the turbosupercharger of the present 
embodiment is described in the following. 
The upper end of the lubrication unit casing 3, in the sense of FIG. 1, is 
provided with a lubrication inlet hole 40 for introducing lubrication oil 
supplied from a lubrication oil pump which is not shown in the drawings to 
the radial bearing metals 13 and the thrust bearing metal 14 by way of a 
lubrication oil passage 41 formed in the interior of the lubrication unit 
casing 3. The lubrication oil which is ejected from each lubricated part 
is led out from a lubrication oil outlet 42 which is defined in the 
lubrication unit casing 3 and is then collected in an oil sump which is 
also not shown in the drawings. 
In order to prevent the lubrication oil, in particular, the part of the 
lubrication oil which is supplied to the thrust bearing metal 14 from 
leaking into the compressor unit by adhering to the outer circumferential 
surface of the bushing 16 and contaminating the engine intake, the outer 
circumferential surface of the bushing 16 passes through a central hole 44 
of the back plate 2 by way of a seal ring 43 and a guide plate 45 having a 
central hole receiving the bushing 16 therethrough is interposed between 
the back plate 2 and the thrust bearing metal 14. The lower portion of 
this guide plate 45 is curved away from the compressor unit. 
The lubrication oil which has flowed out from the thrust bearing metal 14 
is thrown off from the outer circumferential surface of the bushing 16 by 
centrifugal force and is received by the guide plate 45 to be ultimately 
returned to the oil sump. 
The turbine unit of a turbosupercharger of this type can reach a 
substantially high temperature during its operation and control of the 
clearance on either side edge of each moveable vane 34 and possibility of 
mechanical seizure of the moveable vanes 34 due to uneven thermal 
expansion could be a problem. However, according to the present 
embodiment, since the moveable vanes 34 rotate in a gap defined between 
the back plate 23 and the disk portion 28b of the fixed vane member 27 
which is a separate body from the turbine casing 4, the control of the gap 
for the moveable vanes 34 can be favorably accomplished. In particular, 
since the internal ends of the fixed vanes 29 are connected to the back 
plate 23 with threaded bolts 32, the connection between the back plate 23 
and the fixed vane member 27 is highly rigid and the management and 
control of the clearance in the range of the motion of the moveable vanes 
34 can be favorably accomplished. 
And, as shown in FIG. 3, since the width of the gap defined between the 
back plate 23 and the disk portion 28b for accommodating the axial width 
of the moveable vanes 34 in a freely rotatable manner is a in the outer 
periphery and b in the inner periphery (a&lt;b) or, in other words, flares 
out from the outer periphery to the inner periphery, the tendency for the 
inner peripheral portion to deform inwardly due to thermal expansion can 
be compensated for and the mechanical seizure of the moveable vanes 34 can 
be avoided. In other words, when the opening of the variable nozzles is 
small the clearance of the moveable vanes is minimized for a maximum 
turbine efficiency, and when the opening of the variable nozzles is great 
and the performance of the turbine is relatively insensitive to the 
magnitude of the clearance of the moveable vanes is maximized so that the 
possibility of the mechanical seizure of the moveable vanes can be 
eliminated. 
Particularly when the opening degree of the moveable vanes 34 is at a 
minimum or, in other words, when the width of the gap between the moveable 
vanes 34 and the fixed vanes 29 is reduced to g.sub.min, the leakage of 
the exhaust gas from the axial end surfaces of the moveable vanes 34 could 
be a problem. In the present embodiment, the axial dimension of the part 
which receives each of the moveable vanes can be accurately determined 
because the fixed vane member 27 is attached to the back plate 23 at its 
fixed vanes 29 and the leakage of exhaust gas from the axial end surfaces 
of the moveable vanes 34 can be limited to a relatively low level. 
Furthermore, since shoulders 50 and 51 are provided in the back plate 23 
and the opposing surface of the disk portion 28b of the fixed vane member 
27 as best shown in FIGS. 3 and 5 so as to be complementary to the axial 
ends of the moveable vanes 34 as best shown in FIG. 5, the leakage of 
exhaust gas from the axial end portions of the moveable vanes 34 is 
minimized and the efficiency of the turbine can be favorably improved. 
Now the action of the present embodiment is described in the following. 
When the rotational speed of the engine is low and the flow rate of the 
exhaust gas is small, as shown by the solid lines in FIG. 2, by closing 
the moveable vanes 34, the width of the nozzle gaps defined in the 
overlapped portions between the leading edge portions of the fixed vanes 
29 and the trailing edge portions of the moveable vanes 34 is reduced to 
the minimum value g.sub.min. As a result, the flow of the exhaust gas is 
restricted and accelerated to a maximum extent and after turning into a 
spiral flow in the inlet passage 21c between the fixed vane members 27 and 
the turbine wheel 31 reaches the turbine wheel 30 so that the turbine 
wheel 31 is driven by the accelerated exhaust gas and the engine intake 
can be supercharged to the engine even in a low speed range of the engine. 
When the engine speed is high and a sufficient supercharging is taking 
place, the nozzles defined between the fixed vanes 29 and the moveable 
vanes 34 are opened wider as shown by the imaginary lines in FIG. 2. As a 
result, the exhaust gas is not accelerated and the back pressure of the 
engine exhaust system is reduced since the exhaust gas can reach the 
turbine wheel 30 without encountering any significant flow resistance. 
In the above described structure of variable nozzles in which the nozzles 
are defined between neighboring fixed vanes and moveable vanes, the length 
of the overlap L between the leading edge of each fixed vane and the 
trailing edge of the adjacent moveable vane strongly affects the 
performance of the turbine. For instance, if the overlap L along the 
direction of the fluid flow is excessive, the resistance to the fluid flow 
becomes so great that not only the fluid flow efficiency drops but also an 
aerodynamic lift acting upon the moveable vanes could impair the precision 
of control. On the other hand, if the overlap L is too small, the 
smoothing of the fluid flow tends to be insufficient and this also causes 
reduction in the fluid flow efficiency. 
According to the experiments conducted by the inventors based upon such a 
recognition, it was found that a relatively high efficiency can be 
obtained if the ratio of the overlap L relative to the axial width of the 
moveable vanes is from 20 to 60%. In particular, when this ratio is 
between 20 and 30%, it was found that the most favorable results can be 
obtained in terms of efficiency and ill effects of the lift. 
FIGS. 6 to 8 show different embodiments of the present invention and those 
parts corresponding to those of the previous embodiment are denoted by 
like numerals. 
In the embodiment shown in FIG. 6, there are six fixed vanes 29 and six 
moveable vanes 34. In the embodiment shown in FIG. 7, three fixed vanes 29 
and six moveable vanes are provided. In the embodiment shown in FIG. 8, 
two fixed vanes 29 and two moveable vanes 34 are provided. In all of these 
embodiments, each moveable vane 34 is associated with a different one of 
the fixed vanes 29 and defines a substantially smooth airfoil with the 
fixed vane 29. The circumferential positions of the moveable and fixed 
vanes can be freely selected but it is preferred that one of the moveable 
vanes aligns with the inlet opening 21a of the scroll passage 21 as 
exemplified by the embodiments shown in FIGS. 7 and 8. This latter feature 
is advantageous in reducing the flow resistance to the gas introduced into 
the turbine and is of a greater significance as there are a fewer number 
of vanes. 
Thus, according to the present invention, since the flow resistance to the 
fluid flow entering the turbine can be minimized and the range of the 
variation of the variable nozzles can be expanded, improvement of 
controllability of the turbosupercharger can be accomplished and the need 
for a waste gate valve can be eliminated. Additionally, the present 
invention can contribute to the improvement of turbine efficiency and 
improvement of engine performance when the invention is applied to a 
turbosupercharger for the engine. 
Furthermore, according to the present invention, the control and management 
of the clearance of the moveable vanes are simplified with the result that 
a significant advantage can be obtained in improving the facility of 
manufacture and the reliability of the turbine. And, since the clearance 
of the moveable vanes when the opening degree of the variable nozzles is 
at a minimum value is minimized and the efficiency of the turbine can be 
improved. 
Although the present invention has been shown and described with reference 
to the preferred embodiment thereof, it should not be considered as 
limited thereby. Various possible modifications and alterations could be 
conceived of by one skilled in the art to any particular embodiment, 
without departing from the scope of the invention.