Patent Publication Number: US-10329929-B2

Title: Retaining ring axially loaded against segmented disc surface

Description:
BACKGROUND 
     The subject matter disclosed herein generally relates to attaching a disc and cover plate and, more particularly, to attaching a disc and cover plate with a retention ring. 
     Gas turbine engines, such as those used to power modern commercial and military aircrafts, generally include a compressor section to pressurize airflow, a combustor section for burning hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. The airflow flows along a gas path between components through the gas turbine engine. 
     Accordingly, a gas turbine engine includes a plurality of rotating and static components arranged axially along an axis of rotation of the gas turbine engine, in both the compressor section and the turbine section. For example, the gas turbine engine includes a plurality of discs arranged in an axial direction that extend radially outward from the central axis of rotation. These discs also have coverplates that are coupled to the discs. 
     Accordingly there is a desire to find ways to connect the disc and cover plate. 
     SUMMARY 
     According to one embodiment a disc for a gas turbine engine is provided. The disc includes a disc bore including, a groove formed on an axially extending surface of the disc bore, wherein the groove includes a forward surface that extends radially into the disc bore to a groove floor that is cut into the disc bore and extends axially to an aft surface that extends radially outward to at least the axially extending surface of the disc bore, and a scallop formed along at least one surface of the groove, wherein the scallop is configured to provide a flow path, and a disc web that extends radially outward from the disc bore, relative to an axis of rotation of the gas turbine engine. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include wherein the disc bore further includes an interstage coupling disposed on the axially extending surface at a peripheral aft edge of the disc bore that includes a protrusion that extends axially in the aft direction beyond an aft surface of the disc bore. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include wherein the scallop is formed along the aft surface extending radially for a length of the aft surface forming the flow path. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include wherein the scallop is formed along the aft surface and the forward surface forming the flow path. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include further includes a disc blade attachment connected to the disc web at an end of the disc web opposite the disc bore, wherein the disc blade attachment extends radially outward, wherein the disk blade attachment in configured to attach an airfoil to an upper surface of the disc blade attachment, and a cover plate that extends from the disc blade attachment radially along an outside surface of the disc web toward the disc bore creating a cavity between the cover plate and disc web. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include a retaining ring configured to engage with the groove between the cover plate and disc, wherein the retaining ring connects to the interstage coupling of the disc bore and extends into the groove. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include wherein the groove includes a depth that extends radially into the disc bore, and wherein the retaining ring expands into the depth when a compressing force is applied between the cover plate and disc. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include wherein the interstage coupling is configured to couple the disc to a second adjacent disc. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include wherein the groove is located adjacent to the interstage coupling. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the disc may include wherein the cover plate and disc hold the retaining ring in place, and wherein the cover plate and disc hold positions relative to each other when connected using the retaining ring. 
     According to an embodiment, a rotor for a gas turbine engine is provided. The rotor includes at least one disc, the disc including a disc bore including, a groove formed on an axially extending surface of the disc bore, wherein the groove includes a forward surface that extends radially into the disc bore to a groove floor that is cut into the disc bore and extends axially to an aft surface that extends radially outward to at least the axially extending surface of the disc bore, a scallop formed along at least one surface of the groove, wherein the scallop is configured to provide a flow path, and an interstage coupling disposed on the axially extending surface at a peripheral aft edge of the disc bore that includes a protrusion that extends axially in the aft direction beyond an aft surface of the disc bore, and a disc web that extends radially outward from the disc bore, relative to an axis of rotation of the gas turbine engine, a disc blade attachment connected to the disc web at an end of the disc web opposite the disc bore, wherein the disc blade attachment extends radially outward, a cover plate that extends from the disc blade attachment radially along an outside surface of the disc web toward disc bore creating a cavity between the cover plate and disc web, a retaining ring configured to engage with the groove between the cover plate and disc, and an airfoil extending radially outward and connected to an upper surface of the disc blade attachment of the disc. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include, wherein the scallop is formed along the aft surface extending radially for a length of the aft surface forming the flow path. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include, wherein the scallop is formed along the aft surface and the forward surface forming the flow path. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include a plurality of discs, a plurality of disc blade attachments, a plurality of cover plates, a plurality of retaining rings, and a plurality of airfoils. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include, wherein the rotor is one selected from a group consisting of a compressor rotor, a combustor rotor, and a turbine rotor. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include, wherein the retaining ring connects to the interstage coupling of the disc bore and extends into the groove. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include, wherein the groove includes a depth that extends radially into the disc bore, and wherein the retaining ring expands into the depth when a compressing force is applied between the cover plate and disc. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include, wherein the interstage coupling is configured to couple the disc to a second adjacent disc. 
     In addition to one or more of the features described above, or as an alternative, further embodiments of the rotor may include, wherein the groove is located adjacent to the interstage coupling. 
     According to an embodiment, a gas turbine engine is provided. The gas turbine engine includes a turbine section, a combustor section to provide combustion gases to the turbine section, and a compressor section to compress an airflow and direct the compressed airflow toward the combustor, and a rotor disposed in at least one of the turbine section, combustor section, and compressor section, the rotor including at least one disc, the disc including a disc bore including, a groove formed on an axially extending surface of the disc bore, wherein the groove includes a forward surface that extends radially into the disc bore to a groove floor that is cut into the disc bore and extends axially to an aft surface that extends radially outward to at least the axially extending surface of the disc bore, a scallop formed along at least one surface of the groove, wherein the scallop is configured to provide a flow path, and an interstage coupling disposed on the axially extending surface at a peripheral aft edge of the disc bore that includes a protrusion that extends axially in the aft direction beyond an aft surface of the disc bore, and a disc web that extends radially outward from the disc bore, relative to an axis of rotation of the gas turbine engine, a disc blade attachment connected to the disc web at an end of the disc web opposite the disc bore, wherein the disc blade attachment extends radially outward, a cover plate that extends from the disc blade attachment radially along an outside surface of the disc web toward disc bore creating a cavity between the cover plate and disc web, a retaining ring configured to engage with the groove between the cover plate and disc, and an airfoil extending radially outward and connected to an upper surface of the disc blade attachment of the disc. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, that the following description and drawings are intended to be illustrative and explanatory in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  illustrates a schematic cross-sectional view of a gas turbine engine in accordance with one or more embodiments of the present disclosure; 
         FIG. 2  illustrates a schematic cross-sectional view of a disc of a gas turbine engine that is connected to a cover plate in accordance with one or more embodiments of the present disclosure; 
         FIG. 3  illustrates a schematic cross-sectional view of area B of  FIG. 2  including a portion of the disc and cover plate of a gas turbine engine beginning to engage and connect in accordance with one or more embodiments of the present disclosure; 
         FIG. 4A  illustrates a schematic cross-sectional view of a portion of a first disc and a second disc of a gas turbine engine connected using an interstage coupling in accordance with one or more embodiments of the present disclosure; 
         FIG. 4B  illustrates a schematic cross-sectional view of a portion of another first disc and a second disc of a gas turbine engine connected using another interstage coupling in accordance with one or more embodiments of the present disclosure; 
         FIG. 5A  illustrates a schematic cross-sectional view of a portion of a disc of a gas turbine engine that includes a scallop in accordance with one or more embodiments of the present disclosure; 
         FIG. 5B  illustrates a schematic cross-sectional view of a portion of a disc of a gas turbine engine that includes a scallop in accordance with one or more embodiments of the present disclosure; and 
         FIG. 6  illustrates a schematic cross-sectional view of a cover plate of a gas turbine engine that is connected to a disc in accordance with one or more embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As shown and described herein, various features of the disclosure will be presented. Various embodiments may have the same or similar features and thus the same or similar features may be labeled with the same reference numeral, but preceded by a different first number indicating the figure to which the feature is shown. Thus, for example, element “a” that is shown in FIG. X may be labeled “Xa” and a similar feature in FIG. Z may be labeled “Za.” Although similar reference numbers may be used in a generic sense, various embodiments will be described and various features may include changes, alterations, modifications, etc. as will be appreciated by those of skill in the art, whether explicitly described or otherwise would be appreciated by those of skill in the art. 
     In some instances a retaining ring is placed between a disc and cover plate at a point of contact along a web portion of the disc. Specifically, an appendage or protrusion extending axially in an aft direction from the web portion of the disc extends out and then curve radially outward to form a ring groove. These appendages/protrusions provide the point at which a retaining ring can be provided for coupling the disc to a cover plate. The protrusions may be provided extending anywhere along the web portion of the disc. For example, the protrusions, rings, and cover plate connection point can be provided in a mid-section of the web of the disc, at the top of the web portion, at a point in-between, lower along the web, or a combination of positions along the web. 
     However, such a groove forming protrusion extending from a side of the web portion of a disc occupies space that could otherwise be left open or occupied by another feature of a gas engine turbine. Further such a protrusion extending from the side of the web portion of the disc can provide for a more complex disc manufacturing process. Additionally, such a protrusion has restricted structural strength and integrity limited by the thin dimensions of the appendage/protrusion. 
     Embodiments described herein are directed to a retaining ring groove that is submerged into disc of a rotor. The rotor may be a compressor rotor or turbine rotor and may include a plurality of similar discs each having a similar groove. Further, the rotor is part of a gas turbine engine. Particularly, the groove is located on a surface of a disc bore portion or hub portion of the disc. The groove is configured for a retaining ring, for example, a Z ring and may therefore also be called a Z ring groove. 
       FIG. 1  is a schematic illustration of a gas turbine engine  10 . The gas turbine engine generally has a fan  12  through which ambient air is propelled in the direction of arrow  14 , a compressor  16  for pressurizing the air received from the fan  12  and a combustor  18  wherein the compressed air is mixed with fuel and ignited for generating combustion gases. 
     The gas turbine engine  10  further comprises a turbine section  20  for extracting energy from the combustion gases. Fuel is injected into the combustor  18  of the gas turbine engine  10  for mixing with the compressed air from the compressor  16  and ignition of the resultant mixture. The fan  12 , compressor  16 , combustor  18 , and turbine  20  are typically all concentric about a common central longitudinal axis of the gas turbine engine  10 . In some embodiments, the turbine  20  includes one or more turbine stators  22  and one or more turbine rotors  24 . Likewise, the compressor  16  includes one or more compressor rotors  26  and one or more compressor stators  28 . It is to be appreciated that while description below relates to turbine rotors  24 , one skilled in the art will readily appreciate that the present disclosure may be utilized with respect to compressors  16 . 
     As shown, a forward direction is defined as a direction going left, parallel to axis A, toward the fan section  12  found at a forward most position of the gas engine turbine. An aft direction is defined as a direction going to the right, parallel to axis A, back toward the back of the gas engine turbine toward. Particularly, the aft direction extends toward the turbine stators  22  which are in an aft most position. For example, as shown, the ambient air is propelled in the aft direction as shown by arrow  14  which points in the aft direction. 
     Further, components may be provided that extend either radially and/or axially with respect to axis A which is the axis that axially traverses through the center of the gas turbine engine. Particularly, as shown, the axis A traverses axially from a forward to an aft position of the gas turbine engine. Thus, a radial direction, or radially extending, is defined as extending in a direction substantially perpendicular to the axis A. Additionally, if the radial direction is extending toward the axis A that can be defined as radially extending inward, or inward radial expansion. It follows that when the radial direction extends away from the axis A that is defined as radially extending outward, or outward radial expansion. Further, an axial direction, or axially extending, is defined as extending is a direction substantially parallel to the axis A. Additionally, the axial direction may extend in a forward or aft direction. 
       FIG. 2  illustrates a schematic cross-sectional view of a disc apparatus  200  of a gas turbine engine that is connected to a cover plate  206  in accordance with one or more embodiments of the present disclosure. As shown, a disc  201  is provided which is part of a rotor that can be included within any of the rotors in a gas turbine engine as shown in  FIG. 1 . The disc  201  includes at least three components, and may include various surface components. For example, in accordance with one or more embodiments and as shown in  FIG. 2 , the disc  201  includes a disc web  202  forming a middle portion of the disc  201  radially extending between a disc bore  203  and a blade attachment  204 . 
     The disc blade attachment  204  which is attached to an outer diameter of the disc web  202  as shown. That is, the disc blade attachment  204  is connected to an outermost axially extending surface the disc web  202  and extends radially outward from the disc web  202 . An airfoil  222 , which may be for example a blade, connects and extends radially outward from the disc blade attachment. The disc bore  203  is the portion of the disc  201  that is nearest the rotational axis A of the gas turbine engine (e.g., as shown in  FIG. 1 ). As shown, the disc bore  203  is wider, in the axial direction, than both the disc web  202  and the disc blade attachment  204 . Accordingly, there are provided an axially extending surface  212  at the peripheral ends  205  of the disc bore  203  which the disc web&#39;s  202  sides curve and terminate into. 
     On an aft facing side of the disc  201 , a cover plate  206  may be configured and installed to extend from the disc blade attachment  204  to a portion of the disc bore  203 , as discussed below. The cover plate  206  may form an interference fit or other engagement with the disc blade attachment  204  at an outer diameter thereof and form a connection with a plate connector  233  of the disc  201 , as described below. Alternatively, a cover plate  206  may be configured and installed on a forward facing side of the disc  201  to extend from the disc blade attachment  204  to a portion of the disc bore  203 . 
     According to one or more embodiments, the disc also includes a retaining ring  210  that is configured to retain the cover plate  206  in place with respect to the disc  201  when engaged into a groove  214  of a plate connector  233 , which may also be called a groove  233 . In accordance with some embodiments, the retaining ring  210  can be a Z ring, as known in the art. For example, a Z ring is a retaining ring that is substantially z shaped in cross section. The retaining ring  210  is provided along the axially extending surface  212  where the groove  233  meets the interstage coupling  207 . As shown the cover plate  206  extends radially to cover the disc web  202 , or a portion thereof leaving the area along the disc web for other components or elements such as radial snaps discussed and shown below in  FIG. 6 . Rather, the cover plate  206  engages the retaining ring  210  that engaged the plate connector  233 , or groove, on the disc bore  203 . 
     Specifically, looking within area B as shown in  FIG. 2 , in accordance with one or more embodiments, the interstage coupling  207 , which is part of and extends from the disc bore  203 , includes a forward facing side  216 . The interstage coupling  207  also includes a protrusion extending from the forward edge  216  in the aft direction a length of an axially extending surface  215  and is configured to connect the disc apparatus  200  to another disc in the rotor. The forward facing side  216  of the interstage coupling is also an aft surface  216  of the groove  233 . The forward edge  216 , which is also the aft surface  216  of the groove  233 , is where the retaining ring  210  engages along with also potentially engaging with the axially extending surface  215 . The groove  233  is defined by a forward surface  213 , a groove floor  214 , and the aft surface  216 . The groove  233  cuts into the axially extending surface  212  of the disc bore  203  such that the groove floor  214  is depressed within the axially extending surface  212  by a distance equal to the length of the forward surface  213  of the groove  233 . Further, the groove  233  is defined by the aft surface  216  which extends radially further than the forward surface  213  as shown. 
     The forward surface  213  of the groove  233  is configured with a height such that the forward surface  213  prevents the retaining ring from falling, dropping, or walking forward during assembly. Accordingly, one or more embodiments disclosed herein places the groove  233  in an area where it has not been before, particularly, cut into the disc bore  203  geometry rather than extending from the disc web  202 . 
       FIG. 3  illustrates a schematic cross-sectional view of area B of  FIG. 2  including a portion of the disc  201  and cover plate  206  of a gas turbine engine beginning to engage and connect in accordance with one or more embodiments of the present disclosure. The cover plate includes an axial and radial surface for connecting with the retaining ring  310 . The disc  201  includes the disc bore  203  which includes both the groove  333  and an interstage coupling  307 . As shown, the forward surface of the interstage coupling  307  is also the aft surface  316  of the groove  333 . The groove  333  includes the aft surface  316 , a groove floor  314 , and a forward surface  313 . The groove  333  cuts into an axially extending surface  312  of the disc bore  203 . Further, the forward surface extends from the axially extending surface  312  to the groove floor  314  which is shorter than the aft surface  316  which extends from the groove floor  314  up to the axially extending surface  315  of the interstage coupling  307 . 
     As shown, when the retaining ring  310  is assembled it engages to connect the disc  201  and cover plate  206 , the retaining ring  310  engages with the axial and aft surfaces of the cover plate  206 . The retaining ring  310  also engages with the aft surface  316  of the groove  333 . This initial engagement limits and controls the forward and aft movement of the cover plate  206  and disc  201 . 
       FIG. 4A  illustrates a schematic cross-sectional view of a portion of a first disc  401  and a second disc  455  of a gas turbine engine connected using an interstage coupling in accordance with one or more embodiments of the present disclosure. Particularly, as shown the interstage coupling  407  is engaged with an interstage coupling of the second disc  455  such that an aft surface  418  and axial surface  419  of the interstage coupling  407  are engaged with a forward surface  418  and axially extending surface  419  of the second disc  455 . 
     Further, the interstage coupling  407  also includes a cover plate connector, or groove, on a forward side such that the interstage coupling  407  is configured to also connect and engage with a cover plate  406 . The groove includes an aft surface  416  which is also the forward surface of the interstage coupling  407 . Further, the groove includes a groove floor  414  and a forward surface  413  than cuts into an axially extending surface  412  of a disc bore  403 . The groove is configured to engage and connected with a retaining ring and cover plate  406 . Accordingly, rather than providing separate elements, the interstage coupling  407  can function as both the groove/plate connector and an interstage coupling  407  with another disc  455  as shown. 
       FIG. 4B  illustrates a schematic cross-sectional view of a portion of another first disc and a second disc of a gas turbine engine connected using another interstage coupling in accordance with one or more embodiments of the present disclosure. As shown, the interstage coupling between the first disc and second disc may additionally include a second retention ring  460  to prevent interstage decoupling. As shown the other element are substantially similar in location with those shown in  FIG. 4A . For example the interchange coupler surfaces  418  and  419  engage with similar surfaces of the second disc as those shown in  FIG. 4A . However, as shown in this embodiment of  FIG. 4B , the shape of the different elements are slightly varied. Further, according to another embodiment as shown, the second disc may have a forward provided retaining ring  450  configured to connect other elements with the second disc. The second disc also includes a second groove  455  that has a forward surface  453  that is also the aft surface of the second interstage coupling. The groove  455  also includes a groove floor  454  and an aft surface  456 . The groove floor  454  is cut into the surface of the second disc a distance equal to the length of the aft surface  456 . As shown, the groove  455  is configured to engage and connect with the retaining ring  450 . 
       FIG. 5A  illustrates a schematic cross-sectional view of a portion of a disc  501  of a gas turbine engine that includes a scallop  520  in accordance with one or more embodiments of the present disclosure. As shown a retaining ring  510  is engaged and connecting a cover plate  506  with the disc  501 . The scallop  520  is cut into the aft surface  516  of the groove  533 . Accordingly, the scallop  520  provides a flow path for fluid or gas to pass through as indicated by flow line  517 . 
       FIG. 5B  illustrates a schematic cross-sectional view of a portion of a disc  501  of a gas turbine engine that includes a scallop  521  in accordance with one or more embodiments of the present disclosure. As shown a retaining ring  510  is engaged and connecting a cover plate  506  with the disc  501 . The scallop  521  is cut into all three surfaces of the groove  533 . Specifically, as shown the scallop  521  cuts along the forward surface,  513 , the groove floor  514 , and the aft surface  516 . Accordingly, the scallop  521  provides a flow path for fluid or gas to pass through even in the event that the retaining ring  510  is lower and compressed into the groove  533  cavity. 
       FIG. 6  illustrates a schematic cross-sectional view of a cover plate  660  of a gas turbine engine that is connected to a disc apparatus  600  in accordance with one or more embodiments of the present disclosure. As shown, a disc  601  is provided which is part of a rotor that can be included within any of the rotors in a gas turbine engine as shown in  FIG. 1 . The disc  601  includes at least three components, and may include various surface components. For example, in accordance with one or more embodiments and as shown in  FIG. 6 , the disc  601  includes a disc web  602  forming a middle portion of the disc  601  radially extending between a disc bore  603  and a blade attachment  604 . 
     The disc blade attachment  604  which is attached to an outer diameter of the disc web  602  as shown. That is, the disc blade attachment  604  is connected to an outermost axially extending surface the disc web  602  and extends radially outward from the disc web  602 . An airfoil  622 , which may be for example a blade, connects and extends radially outward from the disc blade attachment. The disc bore  603  is the portion of the disc  601  that is nearest the rotational axis A of the gas turbine engine (e.g., as shown in  FIG. 1 ). As shown, the disc bore  603  is wider, in the axial direction, than both the disc web  602  and the disc blade attachment  604 . Accordingly, there are provided an axially extending surface  612  at the peripheral ends  605  of the disc bore  603  which the disc web&#39;s  602  sides curve and terminate into. 
     On an aft facing side of the disc  601 , a cover plate  660  may be configured and installed to extend from the disc blade attachment  604  to a portion of the disc bore  603 , as discussed below. The cover plate  660  may form an interference fit or other engagement with the disc blade attachment  604  at an outer diameter thereof and form a connection with a plate connector  633  of the disc  601 , as described below. Alternatively, a cover plate  606  may be configured and installed on a forward facing side of the disc  601  to extend from the disc blade attachment  604  to a portion of the disc bore  603 . 
     According to an embodiment, a cover plate is provided that uses two radial snaps to transfer load into the disc and has a feature to enable the use of a z-ring (retaining ring) to keep it axially attached to the disc. Additionally, the retaining ring is located in the bore region of the disc. 
     For example, looking within area C as shown in  FIG. 6 , in accordance with one or more embodiments, the cover plate  660  includes an inner surface that faces in a forward direction toward the disc  601  and an outer surface that faces away from the disc  601  in an aft direction. The cover plate  660  extends radially from the groove  633  at the disc bore  603  radially upward along an outside surface of the disc creating a cavity between the cover plate  660  and disc  601 . The cover plate  660  includes two snaps, a first snap  662  and a second snap  663  that are configured to connect to the disc web  602 . Specifically, the first snap  662  extends axially in a forward direction through the cavity formed between the disc  601  and cover plate  660  far enough to connect with a surface of the disc web  602 . Similarly, the second snap  663  extends axially in the forward direction through the cavity far enough to connect with a surface of the disc web  602 . The first snap  662  can also be called an inner snap  662  because it is located radially inward along the body of the cover plate  660  as compared to the second snap  663  which can be call the outer snap  663  because it is located radially further out along the body of the cover plate  660 . 
     The cover plate  660  also extends radially inward to form an attachment protrusion  661  for a retaining ring  610  that secures the cover plate  660  to the disc  601  at the disc bore  603 . The attachment protrusion  661  maintains a similar axial thickness as the other regions  664  and  665  of the cover plate  660 . According to another embodiment, the attachment protrusion  661  may also be a full ring member  661  formed to connect with the retention ring  610 . A full ring member  661  can provide structural benefits. 
     Further, the cover plate  660  includes radially staggered knife edges  666  and  667 . The first knife edge  666  is formed at the top of a protrusion that extends axially in an aft direction and then radially outward. The second knife edge  667  extends from its own protrusion that also extends axially in the aft direction and then radially outward. According to an embodiment, the radially staggered knife edges  666 ,  667  are in close proximity to second snap  663 , which can also be called the outer snap  663 , in order to restrain deflections. 
     Additionally, according to another embodiment, a puller protrusion  668  can be formed at the tip of the attachment protrusion  661 . The puller protrusion extends radially outward from the tip of the attachment protrusion  661  of the cover plate  660 . The puller protrusion may be used to help pull the cover plate  660  away from being engaged with the disc  601 . 
     Further, according to another embodiment, the cover plate  660  can be formed of two substantially straight angled portions  664 ,  665  that extend radially to form the body of the cover plate  660 . This cover plate  660  shape, which includes two substantially straight angled portions  664 ,  665 , may help restrain deflections. Additionally, according to another embodiment, the cover plate  660  can reduce stress and better transfer load to the disc. 
     According to one or more embodiments, the disc also includes a retaining ring  610  that is configured to retain the cover plate  660  in place with respect to the disc  601  when engaged into a groove  614  of a plate connector  633 , which may also be called a groove  633 . In accordance with some embodiments, the retaining ring  610  can be a Z ring, as known in the art. For example, a Z ring is a retaining ring that is substantially z shaped in cross section. The retaining ring  610  is provided along the axially extending surface  612  where the groove  633  meets the interstage coupling  607 . As shown the cover plate  660  extends radially to cover the disc web  602 , or a portion thereof, with two snaps  662  and  663  that connect to the disc web  602 . The cover plate  660  also engages the retaining ring  610  that engaged the plate connector  633 , or groove, on the disc bore  603 . 
     According to one or more embodiments, the interstage coupling  607 , which is part of and extends from the disc bore  603 , includes a forward facing side  616 . The interstage coupling  607  also includes a protrusion extending from the forward edge  616  in the aft direction a length of an axially extending surface  615  and is configured to connect the disc apparatus  600  to another disc in the rotor. The forward facing side  616  of the interstage coupling is also an aft surface  616  of the groove  633 . The forward edge  616 , which is also the aft surface  616  of the groove  633 , is where the retaining ring  610  engages along with also potentially engaging with the axially extending surface  615 . The groove  633  is defined by a forward surface  613 , a groove floor  614 , and the aft surface  616 . The groove  633  cuts into the axially extending surface  612  of the disc bore  603  such that the groove floor  614  is depressed within the axially extending surface  612  by a distance equal to the length of the forward surface  613  of the groove  633 . Further, the groove  633  is defined by the aft surface  616  which extends radially further than the forward surface  613  as shown. 
     The forward surface  613  of the groove  633  is configured with a height such that the forward surface  613  prevents the retaining ring from dropping or walking forward during assembly. Accordingly, one or more embodiments disclosed herein places the groove  633  in an area where it has not been before, particularly, cut into the disc bore  603  geometry rather than extending from the disc web  602 . 
     Thus, in accordance with one or more embodiments, the retaining ring, which may be a Z-Ring, and groove, once provided as disclosed above, can help remove features from the surfaces of the cover plate and the disc web which can reduce the number of life limiting area on the components, or can help free up space previously used by the retaining portion for other features and elements as discussed in one or more embodiments herein. 
     While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.