Axial and radial holding system for the rotor vane of a turbojet engine

A blade holding system including a block 13 formed of an elongated part 15 having a lengthwise slot 18 extending over virtually its entire length. The longitudinal sides 181, 182 have openings 23 that receive an axle 17 holding a flexible strip 16 partially lodged in the slot. The flexible strip has two shanks 25, 26. The end 29 of one of the shanks 26 rests on one end 21 of the elongated part 15, the end 28 of the other shank 25 juts out from the lower plane of the elongated part 15 and, when the block 13 is in place between the blade foot 6 and the dovetail groove 2, is able to rest against the bottom 14 of the groove 2.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention concerns an axial and radial holding assembly for the rotor 
blade of a turbojet engine able to prevent hammering of the blade feet and 
the groove, and more particularly a block that can be housed between the 
blade foot and the bottom of the groove provided in the rim of the rotor 
disk. 
2. Description of the Prior Art 
Axial and radial holding assemblies for blades, such as that described in 
French Pat. No. 2 345 605, consisting of a block that is placed between 
the blade foot and the bottom of the groove so as to hold the upper part 
of the blade foot dovetailed against the side teeth of the groove, with 
the block being held axially by a U-shaped lock cooperating with 
corresponding notches provided in the blade foot and in the teeth of the 
groove, are well-known and the system shown therein is simple and 
effective. To facilitate or even make possible the assembly and 
dismantling of the unit, there nonetheless is some play between the block, 
the blade foot and the bottom of the groove (at least for most blades). 
This play proves to be harmful from the viewpoint of wear. Indeed, during 
self-rotation or low-speed rotation of the rotor, the centrifugal force 
exerted on the blades is no longer sufficient to keep the blade feet 
pressed against both oblique faces of the grooves. 
With each turn, the blades go from a position of resting on one side of the 
seating to a position of resting on the other side. This produces chatter 
and, what is more serious, hammering, which does serious damage to the 
surfaces in contact with one another. If such hammering is difficult to 
accept even for parts that are easily replaceable, such as the blocks or 
even the blades, it is impossible for the rotor disk, for which such 
damage is entirely unacceptable. 
Hence, French Pat. Nos. 2 300 215 and 2 426 151 offer solutions that make 
use of blocks having an elastic part able to maintain permanent contact 
between the blade foot and the groove. The block described in the first 
patent cited consists of three lengthwise, independent parts, two lateral 
parts, and one central part. The two lateral parts have on the ends of two 
adjacent faces a plurality of flanges provided so as to be able to press 
against the front or rear face of the disk, on either side of the groove 
and against the radial ends of the blade feet. These two symmetrical parts 
are introduced into the space between the blade foot and the bottom of the 
groove and are held apart by the central part having a shape approximately 
complementary to the remaining space. This part includes a housing that 
receives an elastic member resting against the bottom of the groove. The 
three parts are unitarily connected with a bolt after being put in place. 
The second patent cited describes a block having two lateral parts 
identical to those of the preceding patent, but a central part consisting 
of two elements and a supplementary locking block. One of the elements 
forms a spacing block that can be elastically distorted in the axial plane 
and cooperates with a groove provided in the small bar forming the other 
element and is intended to be placed against the bottom of the groove. 
Installation of the system is achieved as in the previous case by 
introducing the lateral parts, the small bar, and then the spacing block. 
Then the locking block is placed between the ends of the small bar and the 
spacing block and this presses the spacing block against the small bar and 
the blade feet. A bolt holds the various parts together and assures 
locking engagement therebetween. 
The elastic distortion of the spacing block, when it is in place, develops 
sufficient contact strength to hold the blade foot regardless of the 
rotor's rotation speed. The large number of parts in either of these 
solutions from the prior art nonetheless makes assembly and dismantling of 
the blades a delicate task. 
SUMMARY OF THE INVENTION 
The object of the present invention involves the provision of a holding 
assembly of the same type as those described in the prior art, but having 
a lesser number of parts and above all forming a unit that can be 
installed or removed in a single operation. 
The assembly according to the invention is remarkable in that the block is 
formed as a unit consisting of an elongated part having a lengthwise slot 
extending over virtually its entire length, the lengthwise sides of the 
part having coaxial openings, an axle 17 passing through said openings, a 
flexible strip, held by said axle, housed in the slot and having in 
relation to the axle two shanks, the top and bottom sides of which create 
between them obtuse angles, with the free end of one shank supported 
against one end of the elongated part, and the free end of the other shank 
having a part able to rest on and exert radial pressure against the bottom 
of the dovetail groove.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows in exploded view an axial and radial holding assembly for a 
rotor blade. The rotor disk 1 has formed in its rim a plurality of axial 
grooves 2 with a dovetail section. On the periphery of the disk 1 and 
perpendicular to its upstream face, a plurality of teeth 3 provided 
between the grooves bear notches 4 facing one another, the bottoms of 
which are parallel to the radial plane passing through the middle of the 
groove 2. The blade 5, the foot 6 of which has a dovetail shape 
corresponding to that of the groove 2, has an upstream extension in the 
shape of a flange 7, laterally bearing a plurality of notches 8. 
Assembly of the blade is achieved by sliding the foot 6 in the groove 2 of 
the rotor disk 1. When the end 9 of the foot 6 is flush with the 
downstream face 10 of the disk 1, the notches 8 of the blade flange 7 are 
opposite the notches 4 of the neighboring teeth 3. A U-shaped lock 11, 
equal in thickness to the distance separating the lateral edges of the 
notches 4 in the teeth, has an indentation 12 the upper part of which, 
near the horizontal shank of the U, has a slot. The cross section of this 
slot corresponds to that part of the flange 7 located between the notches 
8. The central part of the indentation has a cross section corresponding 
to the cross section of the block 13. 
Assembly is achieved in accordance with the following steps. After sliding 
the blade foot 6 into the groove 2, the lock 11 is introduced between the 
notches 4 and 8 of the teeth and the blade foot 6. The lock 11 is then 
blocked up against the flange 7. Then the block 13 is introduced into the 
central part of the indentation 12 and between the blade foot 6 and the 
bottom 14 of the groove 2. The lock presses the dovetail part of the blade 
foot against the corresponding parts of the seating constituting the 
groove 2 in the disk 1. 
According to one example of realization of the invention, the block 13 
(FIG. 2) consists of three assembled elements: an elongated part 15, a 
flexible strip 16 and an axle 17, for which the mode of cooperation will 
be described below. The elongated part 15 bears in its longitudinal plane 
of symmetry a slot 18 extending over virtually its entire length. Two 
bridges 190 and 200 are formed at the front and rear ends 19, 20 of the 
part 15. The bridge 200 made at the rear end bears a groove 21, the bottom 
of which has a part approximately parallel to the lower plane of the part 
that can be connected to another part 22 inclined towards the inside of 
the slot 18 and meeting the lower plane. At the front end 19 the part has 
a cross section of lesser height than that of the rear end 20. 
The lengthwise sides 181 and 182 of the part 15 bear two openings 23 
coaxial to an axis perpendicular to the part's longitudinal plane of 
symmetry. The flexible strip 16 is less thick than the slit 18 and 
approximately equal in length to the slot and bears an opening 24 
perpendicular to its longitudinal plane of symmetry. The strip 16 is 
formed on either side of this opening 24 by two shanks 25 and 26, the top 
and bottom sides of which are designated respectively by 251, 261, 252, 
262 and form obtuse angles. The shank 25 bears at its free upstream end 27 
an indentation 28 in the shape of a right-angled dihedron, the planes of 
which are connected by a rounded-off portion 28', and the end of the shank 
26 has a plane boss 29. The function of the indentation 28 and boss 29 
will be explained later. 
The block 13 is formed by introducing the flexible strip 16 into the slot 
18 in the part 15, the boss 29 of the shank 26 lying on the horizontal 
bottom of the groove 21, then interconnecting them by means of the axle 17 
passing through the openings 23 in the block and 24 in the strip 18. In 
this manner the three parts 15, 16, 17 form the block 13 proper. It should 
be noted that the angle created by the shanks of the strip causes the end 
27 to go beyond the lower plane of the block when the part 29 rests on the 
bottom of the groove 21. 
Because the end 27 juts out, in order to introduce the block 13 between the 
blade foot 6 and the bottom 14 of the groove, it is necessary to force 
this end 27 so that it lodges in the slot 18. The end 27 of the strip 16 
is held in this position by a device having means that rest on the top 
face 190 of the end 19 of the part 15 and engage in a notch 30 made in the 
lower face of the front end 27 of the flexible strip 16. The pressure 
exerted simultaneously on the end of the flexible strip 16 and the end of 
the part 15 makes it possible to partially retract inside the slot 18 the 
front end of the flexible strip 16. 
In order to limit the movement of the flexible strip 16, when the part 15 
and the strip 16 are pressed by a tightening device the upstream wall of 
the slot 18 can be slightly extended downstream along an inclined plane 
indicated by the dotted line 180 in FIG. 4. In fact, excessive movement 
towards the outside of the face 251 may make the block 13 too thick to 
allow it to be introduced into the groove 2 of the disk 1. 
When the flexible strip 16 is thus made taut, as previously described the 
block 13 is introduced into the central indentation 12 of the lock 11 
between the blade foot 6 and the bottom 14 of the groove 2 of disk 1. The 
indentation 28 in the end of the flexible strip 16 then caps off the 
upstream face of the rotor disk 1 through the groove 2. 
The device maintaining the pressure between the part 15 and the strip 16 is 
then removed, which places the horizontal face of the indentation 28 
against the bottom 14 of the groove 2 and the vertical face of the 
indentation 28 against the upstream face of the disk 1. As illustrated in 
FIG. 4, the block 13 is thus locked axially, from the upstream side 
towards the downstream side. Locking in the opposite direction, from the 
downstream side towards the upstream side, can be assured in a known 
manner by a flange of the front cap resting against the end 19 of the 
block 13. 
When the strip 16 relaxes, it exerts a pressure against the blade foot 6 by 
means of a boss 31 provided on the strip plumb with the axis of rotation 
and on the bottom 14 of the dovetail groove 2 by the two bosses consisting 
of the horizontal face of the indentation 28, towards the front, on the 
bottom 14 of the groove 2 of the disk 1, and of the resting of the boss 29 
on the part 21 of the rear end of the elongated part 15, this rear end 
itself resting on the bottom 14 of the groove 2 towards the rear of the 
disk 1. 
The elasticity of the strip 16 causes the block 13 to rest (directly 
upstream, indirectly by means of the bridge 200 towards the rear) on the 
bottom of the groove 2. The upper center of the strip 16 comes to rest via 
a boss 31 on the lower median part of the blade foot 6, which prevents 
chatter. 
According to one example of realization, the force exerted is then on the 
order of 200 daN, sufficient to prevent the blade from chattering when the 
rotor turns in autorotation. It would not be going beyond the scope of the 
invention to reverse the bearings of the block 13, particularly with two 
bearings of this unit on the lower part of the blade foot 6 and one 
bearing on the disk 1 towards the middle of the groove 2. 
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.