Safety stop for a variable setting stator blade pivot

The device consists of an arm having structure for attachment to the bottom pivot of a stator blade. Stopping elements are provided in the inner stator ring against which the arm can come to rest. The stopping elements consist of the sides of a circumferential notch formed in the inner surface of the inner ring. A C-shaped molding fastened onto the inner ring makes the notch leak-proof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a safety stop for a variable setting 
stator vane pivot in which the blade is equipped with top and bottom 
pivots, and in which the top pivot, which works within a bearing set in 
the engine housing, is controlled by an orientation system while the 
bottom pivot moves within a bearing set in an inner ring of the engine. 
2. Description of the Prior Art 
The adjustability of the orientation of stator in the various compressor 
stages is particularly desirable when one wishes to attain, for example, 
the greatest possible pressure while retaining a sufficient surging margin 
for the various stages at a given speed. As a result, the vanes of one or 
more compression stages have at least one pivot mounted in a bearing and 
capable of being operated by an operating system. If a mechanical 
connector, e.g., a pin joining two successive levers of the operating 
system, or a pin connecting one of these levers to a stationary element 
such as the housing, should fail to fulfill its connecting function for 
whatever reason (e.g., breakage or loss following disengagement of a 
retaining screw), there may occur either a sudden flapping of the blades, 
resulting in the probable surging of the entire stage, or a sustained 
floating of the vanes, resulting in the nearly certain breakage of one of 
the vanes and destruction of the succeeding rotor stages, and possibly 
even more serious secondary damage. 
An example of variable setting stator blades is found in French Pat. No. 
2,205,952 in which the preliminary compression stage and four upper 
compression stages are equipped with adjustable stator blades. The pivots 
at the top of these blades are operated by a system of rings and levers 
which, using a single control, changes the orientation of the vanes of 
each stage in question. The stator of the preliminary compression stage 
has blades of a relatively large size equipped with a bottom pivot capable 
of absorbing deflecting stress. 
SUMMARY OF THE INVENTION 
The present invention is intended to minimize the problems resulting from a 
break in the linkage and is adapted particularly to variable setting 
stator vanes operated at the top but also having a bottom pivot. 
The invention consists of a cam arm including structure for fixing to the 
bottom pivot, and stop means provided in the inner stator ring, against 
which the arm can come to rest.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows in partial section a part of a compressor stage including a 
stator 1 formed by a ring of vanes 2, each vane having top and bottom 
pivots 3 and 4 whose orientation is operated from the top by a linkage 5 
located outside engine housing 6. A rotor 7 is formed by vanes 8, the 
bases of which are set into rotor disk 9. 
Top pivot 3 turns in a bearing set in the upper ring of housing 6. One of 
the ends of a control rod or lever 10 is fixed to pivot 3, while the other 
end is fixed to link 11 for operating the ring of vanes. 
The safety stop of the invention (FIGS. 2, 3 and 5) consists of at least 
one arm 14 including attachment means for becoming fixed to pivot 4, and 
stop elements 15 and 16 fixed to inner ring 13 to block the rotation of 
arm 14 in case the control mechanism (e.g., 10 and 11) breaks. 
According to the embodiment shown in FIGS. 2, 3 and 4, the end of 
cylindrical pivot 4 at the vane root has at least one, and preferentially 
two, parallel flattened surfaces 17. 
Pivot 4 is held within a bearing 12 consisting of a bushing of 
self-lubricating material fixed within inner stator ring 13 of the 
compressor stage. The radially inner surface 18 of this stator ring 13 is 
provided with a circumferentially extending notch 19 into which projects 
the end of pivot 4, particularly the portion bearing flattened surfaces 
17. The arm 14 is fastened to the end of the pivot 4 by the attachment 
means composed of a rectangular central hole 20 with two opposing curved 
ends corresponding to the shape of the end of the pivot 4 so that the 
pivot can fit therein. When viewed flat (FIG. 4), arm 14 is pill shaped 
with the two rounded peaks 22 and 23 that lie along a line parallel to the 
flat sides of the hole 20 and passing through the center of the arm 14. 
The length of this line is less than the width of notch 19. The angles of 
the arm are set so as to allow the orientation of the vanes to be adjusted 
within a given angular range. In case of breakage of the operating 
elements, the ends of the opposing sides of the arm will abut the stop 
means formed by sides 15 and 16 of notch 19 to limit rotation of the arm. 
In order to ensure that channel 19 will remain leak tight and/or that the 
arm will be securely held in the ring 13, an annular piece 21, e.g., a 
C-shaped piece, is fastened by any known means onto lower stator ring 13. 
In a second embodiment shown in FIG. 5, the spindle of bottom pivot 4 
contains a hexagonal hole 24 with one opening, into which is inserted a 
nipple 25 of comparable size and shape and extending perpendicular to the 
plane of arm 14, of which the nipple forms an integral part. An annular 
C-shaped molding 21 is attached to the inner stator ring 13 to ensure a 
proper seal and, possibly, to support the arm 14 against the pivot. 
In other equivalent embodiments that have not been shown: 
1. The arm may be shaped like a isoceles triangle corresponding to a 
truncated part of the arm disclosed above and having at the middle of its 
base structure by which it can become fixed to the end of the pivot. 
2. The arm may be rectangular, with attachment structure provided at the 
center or at one end of the rectangle. 
3. Stop elements 15 and 16 may consist, for one or more arms, of the walls 
of a recess into which the end of the pivot enters. 
In case of a break of linkage, the vane may swivel suddenly under the 
effect of aerodynamic forces until the ends of arm 14 come up against the 
walls of recess or channel 19 of the ring 13. 
Besides the advantages of eliminating the surging of the stage and breaking 
of vanes, the limiting of the degree of possible accidental play of the 
vane allows limiting of the overall length of the engine. Since the vanes 
can no longer behave like a sail and "turn into the wind," it becomes 
possible to reduce the length of the engine by 5 mm per stage, leading to 
a significant reduction in mass. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.