(19)
(11)EP 2 540 988 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
29.04.2020 Bulletin 2020/18

(21)Application number: 12172156.7

(22)Date of filing:  15.06.2012
(51)International Patent Classification (IPC): 
F01D 11/08(2006.01)

(54)

BLADE OUTER AIR SEAL WITH A PLUG ASSEMBLY AND METHOD

AUSSENDICHTUNG EINER TURBINENSCHAUFEL MIT PFROPFENANORDNUNG UND VERFARHREN

JOINT EXTERNE D'AUBE AVEC ASSEMBLAGE DE BOUCHON ET PROCÉDÉ


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 20.06.2011 US 201113163929

(43)Date of publication of application:
02.01.2013 Bulletin 2013/01

(73)Proprietor: United Technologies Corporation
Farmington, CT 06032 (US)

(72)Inventors:
  • Blaney, Ken F.
    Middleton, NH New Hampshire 03887 (US)
  • Lutjen, Paul M.
    Kennebunkport, ME Maine 04046 (US)

(74)Representative: Dehns 
St. Bride's House 10 Salisbury Square
London EC4Y 8JD
London EC4Y 8JD (GB)


(56)References cited: : 
WO-A1-2009/056788
US-A1- 2009 095 435
US-A- 3 691 924
US-B1- 6 749 384
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND



    [0001] The present application relates to a plug assembly and more particularly to a blade outer air seal (BOAS).

    [0002] Gas turbine engines generally include fan, compressor, combustor and turbine sections positioned along an engine axis of rotation. The fan, compressor, and turbine sections each include a series of stator and rotor blade assemblies. A rotor and an axially adjacent array of stator assemblies may be referred to as a stage. Each stator vane assembly increases efficiency through the direction of core gas flow into or out of the rotor assemblies.

    [0003] An outer case may include a multiple of blade outer air seal (BOAS) segments which provide an outer radial flow path boundary for the core gas to accommodate thermal and dynamic variation. The BOAS segments are subjected to relatively high temperatures and often receive a secondary cooling airflow for temperature control.

    [0004] The BOAS segments may be cast via an investment casting process. In an exemplary casting process, a ceramic casting core defines core legs which extend between edges of the core. The core is placed in a die and wax is molded in the die to form a pattern. The pattern may be shelled, e.g., a stuccoing process to form a ceramic shell, then the wax removed from the shell. Metal is cast in the shell over the core then the shell and core are destructively removed. After core removal, the core legs form as-cast passageways open at both edges of the raw BOAS segment casting. At least some of these core run-out passageways are closed via plug welding or braze pins. Air inlets and outlets to the passageways may then be drilled.

    [0005] US 6749384 B1 discloses a drive rivet that includes a head portion which abuts the outer surface of the first of a plurality of panel members when installed. A shank portion extends from the head portion and includes a plurality of expansible prongs on its distal end which protrude out from the opposite end of the panel members. The shank portion includes at least a first area of substantially constant diameter and a second area of decreased diameter less than that of the first area. An expander pin is driven through a generally elongated bore formed within the drive rivet to urge the expansible prongs outward, which causes the shanks second area of decreased diameter into engagement with the panel members. US2009095435 discloses a blade outer air seal assembly, wherein openings may be closed via plug welding or braze pins.

    SUMMARY



    [0006] The present invention provides a a blade outer air seal of a gas turbine engine as defined in claim 1.

    [0007] The present invention further provides a method of plugging an opening as defined in claim 7.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0008] The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

    Figure 1 is a general sectional diagrammatic view of a gas turbine engine HPT section;

    Figure 2 is a sectional view of a BOAS segment;

    Figure 3 is a sectional view of the BOAS segment;

    Figure 4 is an exploded perspective view of the BOAS segment with a plug assembly therefor;

    Figure 5 is an exploded side view of the BOAS segment with a plug assembly therefor;

    Figure 6 is a partial exploded side view of the plug assembly;

    Figure 7 is a side view of the plug assembly in an assembled condition;

    Figure 8 is an exploded side view of another non-limiting embodiment of a plug assembly;

    Figure 9 is an exploded side view of another non-limiting embodiment of a plug assembly;

    Figure 10 is an exploded side view of another non-limiting embodiment of a plug assembly;

    Figure 11 is a side view of the plug assembly of Figure 10 in an assembled condition.


    DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT



    [0009] Figure 1 schematically illustrates a gas turbine engine 20, illustrated partially as a High Pressure Turbine HPT section 22 disposed along a common engine longitudinal axis A. The engine 20 includes a Blade Outer Air Seal (BOAS) assembly 24 to provide an outer core gas path seal for the turbine section 22. It should be understood that although a BOAS assembly for a HPT is disclosed in the illustrated embodiment, the BOAS assembly may be utilized in any section of a gas turbine engine. The BOAS segment may find beneficial use in many industries including aerospace, industrial, electricity generation, naval propulsion, pumping sets for gas and oil transmission, aircraft propulsion, vehicle engines, and stationary power plants.

    [0010] The turbine section 22 includes a rotor assembly 26 disposed between forward 28 and aft 30 stationary vane assemblies. Outer vane supports 28A, 30A attach the respective vane assemblies to an engine case 32. The rotor assembly 26 includes a plurality of airfoils 34 circumferentially disposed around a disk 36. The distal end of each airfoil 34 may be referred to as the blade tip 34T which rides adjacent to the BOAS assembly 24.

    [0011] The BOAS assembly 24 is disposed in an annulus radially between the engine case 32 and the blade tips 34T. The BOAS assembly 24 generally includes a blade outer air seal (BOAS) support 38 and a multiple of blade outer air seal (BOAS) segments 40 mountable thereto (Figures 2 and 3). The BOAS support 38 is mounted within the engine case 32 to define forward and aft flanges 42, 44 to receive the BOAS segments 40. The forward flanges 42 and the aft flanges 44 may be circumferentially segmented to receive the BOAS segments 40 in a circumferentially rotated and locked arrangement as generally understood. It should be understood that various interfaces may alternatively be provided.

    [0012] Each BOAS segment 40 includes a body 46 which defines a forward interface 48 and an aft interface 50. The forward interface 48 and the aft interface 50 respectively engage the flanges 42, 44 to secure each individual BOAS segment 40 thereto.

    [0013] Each BOAS segment 40 includes one or more cavities 52 to receive a secondary cooling airflow S. It should be understood that various alternative cavity and passageway arrangements may be provided. Each cavity 52 may be formed through, for example, an investment casting process.

    [0014] With reference to Figure 4, the investment casting process typically requires one or more core run out openings 60 be plugged with a plug assembly 62 to assure performance of the BOAS segment 40. It should be understood that although the plug assembly 62 is used to the plug the core run out opening 60 of a BOAS segment 40, the plug assembly 62 may be utilized in various other components.

    [0015] The core run-out opening 60 generally includes a bore portion 64 and a bore anti-liberation portion 66. The bore anti-liberation portion 66 in the disclosed non-limiting embodiment, is a reduced diameter portion adjacent to the innermost section of the bore portion 64. In the disclosed, non-limiting embodiment, the bore anti-liberation portion 66 includes a radially inward directed shoulder 68 (also illustrated in Figure 5).

    [0016] The plug assembly 62 generally includes a cup 70 and a wedge 72. The cup 70 is inserted along an axis C of the as-cast core run out opening 60. The cup 70 includes a cup portion 74 and a cup anti-liberation portion 76 at an end section thereof. The cup anti-liberation portion 76 in the disclosed non-limiting embodiment may include a first reduced diameter portion 78 and a second reduced diameter portion 80. The first reduced diameter portion 78 and the second reduced diameter portion 80 define a diameter smaller than the cup portion 74. The first reduced diameter portion 78 defines a closed end section of the cup 70 and defines a diameter greater than the second reduced diameter portion 80. That is, the second reduced diameter portion 80 is the smallest diameter and is axially located generally in line with the radially inward directed shoulder 68.

    [0017] With reference to Figure 6, once the cup 70 is located into the core run-out opening 60 such that the cup portion 74 abuts the radially inward directed shoulder 68 and the second reduced diameter portion 80 is axially located generally in line with the radially inward directed shoulder 68, the wedge 72 is pressed into the cup 70. As the wedge 72 is pressed into the cup 70, the wedge 72 expands the cup 70 into a press fit with the bore portion 64 (Figure 7). The wedge 72, when pressed into the cup 70, also expands the first reduced diameter portion 78 and the second reduced diameter portion 80 relative to the radially inward directed shoulder 68 such that the first reduced diameter portion 78 defines a diameter greater than the radially inward directed shoulder 68. The cup 70 is thereby further locked in place through the interaction of the cup anti-liberation portion 76 and the bore anti-liberation portion 66.

    [0018] The wedge 72 may be of various shapes such as a pin shape to provide a flush fit with the core run out opening 60 or a ball shape wedge 72' (Figure 8) should a flush fit not be required. The wedge 72" may additionally include a wedge body 82 and a protrusion 84 which facilities expansion of the first reduced diameter portion 78 and the second reduced diameter portion 80 (Figure 9). The protrusion 84 extends from a distal end of the wedge body 82 but may define a lesser diameter than the wedge body 82. The protrusion 84 may be of various shapes such as cylindrical, bull nose, round nose, conical, frustro-conical, angular or other shape which facilities expansion of the first reduced diameter portion 78 and the second reduced diameter portion 80.

    [0019] With reference to Figure 10, an alternate non-limiting embodiment of the cup 70' includes an axial slit 86 which extends at least partially along the length of the cup 70'. The axial slit 86 facilitates expansion of the first reduced diameter portion 78 and the second reduced diameter portion 80 of the cup 70' (Figure 11).

    [0020] The plug assembly provides a consistent robust method which is less reliant on cleaning and surface preparation than brazing. The plug assembly is also less expensive since brazing/welding operation isn't required. Alternatively, brazing may be used as a redundant retention and need not be the primary retaining method. Without brazing, there is no need for heat treat which provides a quicker installation without need of a high proficiency worker. Moreover, the plug assembly may provide materials with higher temperature capability than with metallurgical bond.

    [0021] It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

    [0022] Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.

    [0023] The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The disclosed embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.


    Claims

    1. A blade outer air seal (BOAS) of a gas turbine engine, comprising:

    a bore (60) which defines a bore portion (64) and a bore anti-liberation portion (66) along an axis; and

    a plug assembly (62) received in said bore (60), said plug assembly comprising:

    a cup (70;70') which defines a cup portion (74) and a cup anti-liberation portion (76) along an axis, wherein said cup (70') includes an axial slit (86) extending at least partially along the length of the cup; and

    a wedge (72;72';72") mountable within said cup portion (74) to at least partially radially expand said cup anti-liberation portion (76), wherein said wedge is mountable within said cup portion (74) to engage said cup anti-liberation portion (76) with said bore anti-liberation portion (66), wherein

    said cup anti-liberation portion includes a first reduced diameter portion (78) and a second reduced diameter portion (80) which each defines a diameter smaller than a diameter defined by said cup portion (74), said first reduced diameter portion (78) defines a closed end section of said cup (74), and wherein said first reduced diameter portion (78) defines a diameter greater than a diameter of said second reduced diameter portion (80), and

    said bore anti-liberation portion (66) defines a radially inward directed shoulder (68), said second reduced diameter portion axially aligned with said radially inward directed shoulder (68).


     
    2. The BOAS as recited in claim 1, wherein said wedge (72) is a pin.
     
    3. The BOAS as recited in any preceding claim, wherein said wedge includes a wedge body (82) and a protrusion (84) that extends from a distal end of said wedge body (82).
     
    4. The BOAS as recited in any preceding claim, wherein said wedge includes a wedge body (82) and a wedge protrusion (84) that extends from a distal end of said wedge body (82), said wedge protrusion (84) defines a lesser diameter than said wedge body (82).
     
    5. The BOAS as recited in any preceding claim, wherein said wedge (72) is a pin, said pin (72) flush with an end of said bore (60).
     
    6. The BOAS as recited in any preceding claim, wherein said bore (60) is within a Blade Outer Air Seal (BOAS) segment.
     
    7. A method of plugging an opening (64) in a blade outer air seal (BOAS) of a gas turbine engine comprising:

    pressing a wedge (72) into a cup (70) to at least partially radially expand a cup anti-liberation portion (76) and engage the cup anti-liberation portion (76) with a bore anti-liberation portion (66); and

    forming a bore with a bore portion (64) and the bore anti-liberation portion (66) along an axis,

    characterized in that:

    said cup anti-liberation portion includes a first reduced diameter portion (78) and a second reduced diameter portion (80) which each define a diameter smaller than a diameter defined by said cup portion (74), said first reduced diameter portion (78) defines a closed end section of said cup (74), and wherein said first reduced diameter portion (78) defines a diameter greater than a diameter of said second reduced diameter portion (80), and

    said bore anti-liberation portion (66) defines a radially inward directed shoulder (68), said second reduced diameter portion axially aligned with said radially inward directed shoulder (68).


     
    8. The method as recited in claim 7, further comprising pressing the wedge (72;72';72") and the cup (70;70') flush into the bore portion (64).
     
    9. The method as recited in claim 8, further comprising pressing the wedge (72;72';72") into the bore until a wedge body (82) abuts the radially inward directed shoulder (68) and a wedge protrusion (84) axially extends at least partially beyond the radially inward directed shoulder (68).
     


    Ansprüche

    1. Außendichtung einer Turbinenschaufel (blade outer air seal - BOAS) eines Gasturbinentriebwerks, umfassend:

    eine Bohrung (60), die einen Bohrabschnitt (64) und einen Bohrantibefreiungsabschnitt (66) entlang einer Achse definiert; und

    eine Pfropfenanordnung (62), die in der Bohrung (60) aufgenommen ist, wobei die Pfropfenanordnung Folgendes umfasst:

    eine Schale (70; 70'), die einen Schalenabschnitt (74) und einen Schalenantibefreiungsabschnitt (76) entlang einer Achse definiert, wobei die Schale (70') einen axialen Schlitz (86) beinhaltet, der sich zumindest teilweise entlang der Länge der Schale erstreckt; und

    einen Keil (72; 72', 72"), der innerhalb des Schalenabschnittes (74) montierbar ist, um den Schalenantibefreiungsabschnitt (76) zumindest teilweise radial zu erweitern, wobei der Keil innerhalb des Schalenabschnittes (74) montierbar ist, um den Schalenantibefreiungsabschnitt (76) mit dem Bohrantibefreiungsabschnitt (66) in Eingriff zu nehmen,

    wobei

    der Schalenantibefreiungsabschnitt einen ersten Abschnitt (78) mit reduziertem Durchmesser und einen zweiten Abschnitt (80) mit reduziertem Durchmesser beinhaltet, die jeweils einen Durchmesser definieren, der kleiner als ein Durchmesser ist, der durch den Schalenabschnitt (74) definiert wird, wobei der erste Abschnitt (78) mit reduziertem Durchmesser einen geschlossenen Endabschnitt der Schale (74) definiert und wobei der erste Abschnitt (78) mit reduziertem Durchmesser einen Durchmesser definiert, der größer als ein Durchmesser des zweiten Abschnittes (80) mit reduziertem Durchmesser ist, und

    der Bohrantibefreiungsabschnitt (66) eine radial nach innen gerichtete Schulter (68) definiert, wobei der zweite Abschnitt mit reduziertem Durchmesser axial auf die radial nach innen gerichtete Schulter (68) ausgerichtet ist.


     
    2. BOAS nach Anspruch 1, wobei der Keil (72) ein Stift ist.
     
    3. BOAS nach einem vorhergehenden Anspruch, wobei der Keil einen Keilkörper (82) und einen Vorsprung (84) beinhaltet, der sich von einem distalen Ende des Keilkörpers (82) erstreckt.
     
    4. BOAS nach einem vorhergehenden Anspruch, wobei der Keil einen Keilkörper (82) und einen Keilvorsprung (84) beinhaltet, der sich von einem distalen Ende des Keilkörpers (82) erstreckt, wobei der Keilvorsprung (84) einen geringeren Durchmesser als der Keilkörper (82) definiert.
     
    5. BOAS nach einem vorhergehenden Anspruch, wobei der Keil (72) ein Stift ist, wobei der Stift (72) bündig mit einem Ende der Bohrung (60) ist.
     
    6. BOAS nach einem vorhergehenden Anspruch, wobei sich die Bohrung (60) innerhalb eines Segments einer Außendichtung einer Turbinenschaufel (BOAS) befindet.
     
    7. Verfahren zum Verschließen einer Öffnung (64) in einer Außendichtung einer Turbinenschaufel (BOAS) eines Gasturbinentriebwerks, umfassend:

    Drücken eines Keils (72) in eine Schale (70), um einen Schalenantibefreiungsabschnitt (76) zumindest teilweise radial zu erweitern und den Schalenantibefreiungsabschnitt (76) mit einem Bohrantibefreiungsabschnitt (66) in Eingriff zu nehmen; und

    Bilden einer Bohrung mit einem Bohrabschnitt (64) und dem Bohrantibefreiungsabschnitt (66) entlang einer Achse,

    dadurch gekennzeichnet, dass:

    der Schalenantibefreiungsabschnitt einen ersten Abschnitt (78) mit reduziertem Durchmesser und einen zweiten Abschnitt (80) mit reduziertem Durchmesser beinhaltet, die jeweils einen Durchmesser definieren, der kleiner als ein Durchmesser ist, der durch den Schalenabschnitt (74) definiert wird, wobei der erste Abschnitt (78) mit reduziertem Durchmesser einen geschlossenen Endabschnitt der Schale (74) definiert und wobei der erste Abschnitt (78) mit reduziertem Durchmesser einen Durchmesser definiert, der größer als ein Durchmesser des zweiten Abschnittes (80) mit reduziertem Durchmesser ist, und

    der Bohrantibefreiungsabschnitt (66) eine radial nach innen gerichtete Schulter (68) definiert, wobei der zweite Abschnitt mit reduziertem Durchmesser axial auf die radial nach innen gerichtete Schulter (68) ausgerichtet ist.


     
    8. Verfahren nach Anspruch 7, ferner umfassend ein Drücken des Keils (72; 72'; 72") und der Schale (70; 70') bündig in den Bohrabschnitt (64).
     
    9. Verfahren nach Anspruch 8, ferner umfassend ein Drücken des Keils (72; 72'; 72") in die Bohrung, bis ein Keilkörper (82) an die radial nach innen gerichtete Schulter (68) stößt und sich ein Keilvorsprung (84) axial zumindest teilweise über die radial nach innen gerichtete Schulter (68) hinaus erstreckt.
     


    Revendications

    1. Joint externe d'aube (BOAS) d'un moteur à turbine à gaz, comprenant :

    un alésage (60) qui définit une partie d'alésage (64) et une partie anti-libération d'alésage (66) le long d'un axe ; et

    un assemblage de bouchon (62) reçu dans ledit alésage (60), ledit assemblage de bouchon comprenant :

    une coupelle (70 ; 70') qui définit une partie de coupelle (74) et une partie anti-libération de coupelle (76) le long d'un axe, dans lequel ladite coupelle (70') comprend une fente axiale (86) s'étendant au moins partiellement le long de la longueur de la coupelle ; et

    un coin (72 ; 72' ; 72") pouvant être monté à l'intérieur de ladite partie de coupelle (74) pour élargir au moins partiellement radialement ladite partie anti-libération de coupelle (76), dans lequel ledit coin peut être monté à l'intérieur de ladite partie de coupelle (74) pour mettre en prise ladite partie anti-libération de coupelle (76) avec ladite partie anti-libération d'alésage (66),

    dans lequel

    ladite partie anti-libération de coupelle comprend une première partie au diamètre réduit (78) et une seconde partie au diamètre réduit (80) qui définissent chacune un diamètre plus petit qu'un diamètre défini par ladite partie de coupelle (74), ladite première partie au diamètre réduit (78) définit une section d'extrémité fermée de ladite coupelle (74), et dans lequel ladite première partie au diamètre réduit (78) définit un diamètre supérieur à un diamètre de ladite seconde partie au diamètre réduit (80), et

    ladite partie anti-libération d'alésage (66) définit un épaulement dirigé radialement vers l'intérieur (68), ladite seconde partie au diamètre réduit étant alignée axialement avec ledit épaulement dirigé radialement vers l'intérieur (68).


     
    2. BOAS selon la revendication 1, dans lequel ledit coin (72) est une broche.
     
    3. BOAS selon une quelconque revendication précédente, dans lequel ledit coin comprend un corps de coin (82) et une saillie (84) qui s'étend depuis une extrémité distale dudit corps de coin (82).
     
    4. BOAS selon une quelconque revendication précédente, dans lequel ledit coin comprend un corps de coin (82) et une saillie de coin (84) qui s'étend depuis une extrémité distale dudit corps de coin (82), ladite saillie de coin (84) définit un diamètre plus petit que ledit corps de coin (82).
     
    5. BOAS selon une quelconque revendication précédente, dans lequel ledit coin (72) est une broche, ladite broche (72) affleurant avec une extrémité dudit alésage (60).
     
    6. BOAS selon une quelconque revendication précédente, dans lequel ledit alésage (60) se trouve dans un segment de joint externe d'aube (BOAS).
     
    7. Procédé de colmatage d'une ouverture (64) dans un joint externe d'aube (BOAS) d'un moteur à turbine à gaz,
    comprenant :

    la pression d'un coin (72) dans une coupelle (70) pour élargir au moins partiellement radialement une partie anti-libération de coupelle (76) et mettre en prise la partie anti-libération de coupelle (76) avec une partie anti-libération d'alésage (66) ; et

    la formation d'un alésage doté d'une partie d'alésage (64) et de la partie anti-libération d'alésage (66) le long d'un axe,

    caractérisé en ce que :

    ladite partie anti-libération de coupelle comprend une première partie au diamètre réduit (78) et une seconde partie au diamètre réduit (80) qui définissent chacune un diamètre plus petit qu'un diamètre défini par ladite partie de coupelle (74), ladite première partie au diamètre réduit (78) définit une section d'extrémité fermée de ladite coupelle (74), et dans lequel ladite première partie au diamètre réduit (78) définit un diamètre supérieur à un diamètre de ladite seconde partie au diamètre réduit (80), et

    ladite partie anti-libération d'alésage (66) définit un épaulement dirigé radialement vers l'intérieur (68), ladite seconde partie au diamètre réduit étant alignée axialement avec ledit épaulement dirigé radialement vers l'intérieur (68).


     
    8. Procédé selon la revendication 7, comprenant en outre la pression du coin (72 ; 72' ; 72") et de la coupelle (70 ; 70') affleurant dans la partie d'alésage (64).
     
    9. Procédé selon la revendication 8, comprenant en outre la pression du coin (72 ; 72'; 72") dans l'alésage jusqu'à ce qu'un corps de coin (82) bute contre l'épaulement dirigé radialement vers l'intérieur (68) et qu'une saillie de coin (84) s'étende axialement au moins partiellement au-delà de l'épaulement dirigé radialement vers l'intérieur (68).
     




    Drawing




















    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description