BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of gas turbine engines or turbo machines such as compressors, and more particularly, to a blade or vane that is removably detachable to a rotor disc.
2. Description of the Related Art Including Information Disclosed Under 37 C.F.R. 1.97 and 1.98
A blade or a vane 10 in the Prior Art is attached to a rotor disc 12 by a fir tree configuration as shown in FIG. 5. The blade or vane 10 has a root portion with a fir tree configuration that slides within a slot 14 of the rotor disc 12. The root of the blade or vane is slidably inserted into the slot 14 of the rotor disc 12 along the rotational axis of the disc, and then locked in place. This arrangement provides support for the blade in the disc such that centrifugal force acting to pull the blade radially outward from the disc during rotation does not occur. U.S. Pat. No. 3,378,230 issued to Toomey on Apr. 16, 1968 shows this arrangement, in which the slots are aligned with the rotational axis of the rotor disc.
One problem with this arrangement is when a blade needs to be removed from the disc. If the axial length of the root of the blade is greater than the spacing between adjacent rotor discs, then the root cannot be completely removed from the slot. In order to remove the blade, the adjacent rotor disc must also be removed or moved away from the other disc to increase the spacing. Having to remove a rotor disc is very time consuming.
The U.S. Pat. No. 6,582,195 issued to Davidson on Jun. 24, 2003 shows a Compressor Rotor Blade Spacer Apparatus, where a rotor includes slots to accept blade roots, the slots being offset by an angle of about 40 degrees with respect to the rotational axis of the rotor disc. However, the slots are not curved but are straight.
U.S. Pat. No. 4,419,052 issued to Stamm on Dec. 6, 1983 also shows a rotor disc having blades attached to slots arranged in the disc, where the slots are offset at an angle from the rotational axis of the disc. In Stamm, the slots are not fir tree shaped, however, and thus cannot be curved.
In the above prior art turbo machines, the removal of one rotor blade requires that the rotor discs be disassembled in order that the one blade can be slid out of the disc slot thus, there is a need in the art for an apparatus that will alow for one ro more rotor blades (or vanes) to be removed from the rotor disc without the need to disassemble the rotor discs.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide a blade root arrangement with a shape such that the blade can be removed from a rotor disc slot without the need to remove or adjust a spacing between adjacent discs. This is accomplished by providing for the slot in the disc and the root of the blade to have an arched (or, curved) shaped such that a center of rotation is located at some point above the blade root such that the blade root can be rotated out of the slot without the root bumping into an adjacent rotor disc. The blades of one disc are also positioned between blades of the adjacent disc so that the former blades can be pivoted into position without abutting the blade of the later disc.
An additional object the instant invention is to provide a spring loaded pin assembly to secure the blade root within the disc slot. A pin extends through a hole in both the root and the slot such that a pin can extend into both holes and prevent the root from moving along the slot. The pin is biased by a spring into the locked position, which is also the direction that centrifugal forces would force the pin during rotation of the disc. A second pin can be inserted through an opening of the hole in the disc to push the pin against the bias of the spring such that the pin is extended completely with the hole of the root. In this way the root can be rotated out of the slot and removed.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 shows a cross section view of a rotor disc arrangement of the present invention.
FIG. 2 shows a cross section view of a spring-biased pin that secures a blade root within a rotor disc slot of the present invention.
FIG. 3 shows front view of a rotor disc with the slot opening on the disc face of the present invention.
FIG. 4 shows a top view of the rotor disc of the present invention with the slot and a blade mounted in the slot, where an axis of the slot and root is offset about 15 degrees from the axial centerline of rotation of the rotor disc.
FIG. 5 shows side view of a rotor disc arrangement of the prior art.
FIG. 6 shows a cross sectional view of a non-preferred embodiment of the present invention, in which the slot in the rotor disc is not curved but straight and angled from the disc surface.
FIG. 7 shows a blade root and disc slot of the present invention having a curvature centered at a point midway along the blade and at a point located above a tip of the blade.
DETAILED DESCRIPTION OF THE INVENTION
A gas turbine engine includes a series of rotor discs 20 each having multiple blades or vanes 22 extending outward from an outer surface (FIG. 1). The rotor discs 20 are usually located adjacent to one another with little or no spacing between adjacent discs. Each rotor disc 20 includes a number of slots 24 that open out on the outer surface 26 of the disc 20. These slots 24 receive a root 28 of a blade or vane 22. The slots 28 in the disc 20 are curved instead of straight as in the prior art of FIG. 5. The curvature is from a point radially outward of the rotor disc surface 26 such that one opening of the slot is on the outer surface 26 of the rotor disc 20, while the opposite opening is on the side 30 (see FIG. 3) of the rotor disc. The root is disclosed as having a fir tree configuration. A fir tree configuration is well known in the art of turbomachinery blades. For the purpose of this disclosure, the term “fir tree” is considered to be any shape in which the root can have one or more zip zag portions that would provide an abutment face to prevent the blade and root from being pulled out of the slot along a direction parallel to the longitudinal axis of the blade.
The center of curvature for the slot 24 is preferably located along the blade from a midpoint of the blade to a point just beyond the tip of the blade, as seen in FIG. 7. The point of curvature is preferably located above the blade root and between the rotor disc ends as represented by the vertical lines in FIG. 7. Point 41 in FIG. 7 represents a center of curvature for a root at a point about midway along the blade, while point 42 represents a center of curvature for a root at a point above the blade tip. Both points of curvature are located within vertical lines passing through the disc ends. The purpose of locating the center of curvature within the rotor disc ends in to ensure that the root (and slot) curvature on the right end of the disc (as viewed in FIG. 7) is directed upward in the Figure. This reduces the desire for the root to slide within the slot as described later in this disclosure.
In some situations, the blade cannot pivot far from above the rotor disc in which it is mounted. The blade on the row one disc may not have the space to pivot to a point above the row two disc because of interference with blades. In this case, the slot and root curvature would be located above the blade tip to form a large curvature. The blade could then be pivoted into place without the blade tip passing over the row two disc. In the situation where the blade on rotor disc one could be pivoted between blades on rotor disc two (the blade will pivot into a space between adjacent blades on the rotor two disc), the curvature of the slot could be centered at a point midway on the blade.
The blade or vane 22 includes a root portion having a cross sectional shape identical to the cross sectional shape of the slot 24, and with the same curvature as that of the slot 24. The meaning of “the same cross sectional shape” is meant to mean that the blade root can be slid into the disc slot without undue interference, but with enough grip that the blade root is secured within the slot against centrifugal forces due to rotation of the disc and blade. The curvature of the slot and root is set such that the blade can be rotated out of the slot without the blade interfering with an adjacent blade.
Each slot 24 and root has a hole 32 (see FIG. 2) aligned such that a pin 34 can be moved into each hole. The pin is biased by a spring 36 in a direction in which centrifugal forces would force the pin 34 to move during rotation of the rotor disc. The hole 32 in the root of the blade 22 has an axial length less than the axial length of the pin 34. An additional hole 38 in the blade root 28 extends from the end of the first hole in the root, but with a diameter smaller than the first hole. This second or additional hole 38 extends out the surface of the blade root 28. Its purpose will be described below. When the pin 34 is biased by the spring 36 into contact with a bottom of the hole 32 in the slot, the pin 34 will be located in both holes such that rotation of the blade root within the disc slot is prevented.
The axial length of the hole 32 in the disc slot is greater than the axial length of the pin 34 such that the pin 34 can be moved completely into the hole 32 of the disc slot 24. An external tool or pin (not shown) can be inserted into the second hole 38 in the blade root 28 for the purpose of displacing the pin 34 into the slot hole and completely out of the root hole such that the blade 22 can be rotated out of the rotor disc slot 24 and removed.
An axis of the slot 24 in the rotor disc 12 is offset about 15 degrees from an axis passing parallel to a rotational axis 40 of the rotor disc as shown in FIG. 4. By offsetting the slot 24 axis, a blade with pivot into a space located between adjacent blades in an adjacent rotor disc. This offset will prevent the blade being inserted or removed from hitting one of the secured blades. The offset angle will be determined such that a tip of the blade would pivot toward a point midway between adjacent secured blades. The slot offset could be eliminated if the blades are of such length that the blade being removed will not hit or bump up against a secure blade in an adjacent rotor disc.
FIG. 6 shows an additional embodiment of the present invention, although this embodiment is not desired. In FIG. 6, the slot is straight (as opposed to curved) but angled with respect to the rotational axis of the disc. The root of the blade is also straight and angled to slide within the slot. In this embodiment, the blade and root could be inserted into the slot of the disc without removing adjacent discs. However, in this embodiment, rotational forces would act to pull the blade away from the rotor disc. Because of the angled slot surface, the resulting force to hold the blade and root within the slot would be so great that a large portion of the root would be needed to provide a lock. The preferred embodiment of the present invention is the above described curved slot and root. The curvature provides for a better surface on which the reactionary forces due to the rotation of the blade would act. As can be seen in FIG. 1, the center of rotation for the slot is above and in-between the two ends of the slot in the disc. The curvature of the slot at the right side of the rotor disc is in the upward direction with respect to the figure. Thus, the slot greatly reduces the root from “wanting to” slide within the slot under the centrifugal loads as would be the case in the FIG. 6 embodiment. Each series of rotors will have a similar arrangement of slots to accommodate blades or vanes. Under the arrangement of the instant invention, blades or vanes can be removed from the respective disc without the need to disassemble the rotor disc.
The rotor discs of the present invention shows the blades extending outward from the rotational center of the discs. However, the practice can also be applied to blades or vanes that extend radially inward from a mounting surface.
Patent Application
20060251522
