T 0440/16 14-10-2022

1. Inventive step (Article 56 EPC)

1.1 D2 in combination with the technical teaching of D4

1.1.1 D2 discloses the following features of claim 1:

A cooled airfoil (14) within a gas turbine engine (col. 1, lines 7 to 8) comprising:

a rib (forward bridge, 26) which at least partially defines a forward cavity (the 2nd cavity from the left in Fig. 2) within an airfoil (14), said forward cavity in communication with a cooling circuit flow path (serpentine flow circuit 34; col. 3, lines 13 to 38); and

at least one opening (cross-over hole, 42) through said rib (26), wherein said at least one opening (42) communicates with a leading edge cavity (leading edge flow channel, 32) adjacent said forward cavity;

said cooled airfoil (14) further comprises:

a multiple of turbulators (46) within said leading edge cavity (32), said at least one opening (42) adjacent said multiple of turbulators (46);

wherein said turbulators (46) are defined on the inner wall (see Fig. 2) of said leading edge cavity (32);

wherein said multiple of turbulators (46) are opposite a multiple of gill holes (50).

1.1.2 D2 fails to disclose (in any single embodiment):

- a multiple of showerhead holes within a leading edge of said leading edge cavity;

- said at least one opening (42 in D2) being offset within said forward cavity relative a longitudinal axis of said airfoil; and

- turbulators in the form of angled trip strips defined along a pressure side (i.e. the concave surface side) of the cooled airfoil.

1.1.3 The appellant's contention that the showerhead holes were also known from D2 is not accepted. Col. 4, lines 3 to 13 of D2 discloses a primary embodiment without showerhead cooling holes and further mentions 'other embodiments' of the invention which include such holes. The skilled person would however be unsure which features of the primary embodiment would remain unmodified when including the showerhead holes.

1.1.4 In this regard the respondent referred to the low cycle fatigue resulting from the showerhead holes being included in the leading edge of the airfoil (see col. 4, lines 11 to 13) and the statement that "this would then have to be addressed". The Board concurs that this issue would clearly need to be considered by the skilled person, D2 providing no guidance as to what design impacts this may have on e.g. the fins 44 or the turbulators 46, 48 in the leading edge flow channel 32.

1.1.5 Beyond this, in the primary embodiment of D2, the crossover holes 42 direct the cooling air 40 onto the fins 44 at the leading edge of the channel 32 for dispersing heat from the airfoil sidewalls (see col. 3, lines 39 to 48). Thereafter the cooling air is directed to the gill holes 50 for emitting cooling air from the channel 32 (col. 3, lines 60 to 65). It is thus evident that introducing showerhead holes at the leading edge of the airfoil would materially affect the cooling air flow in the channel 32 such that the fins 44 and gill holes 50 would be expected to require redesigning.

1.1.6 Consequently, contrary to the opinion of the appellant, should the showerhead holes be included in the airfoil of D2, there is no unambiguous disclosure of which features of the primary embodiment would still be included in such an embodiment. The Board thus finds there to be no unambiguous disclosure in D2 of the features of claim 1 indicated to be known in point 1.1.1 above in combination with the showerhead holes.

1.1.7 Based on the features in point 1.1.2 differentiating claim 1 over D2, the objective technical problem to be solved may be seen as being 'how to improve the cooling efficiency in the leading edge cavity of the airfoil of D2'. Both parties essentially accepted this problem as being objective.

1.1.8 The Board finds the skilled person not to be guided to the necessary modification of D2 through the technical teaching of D4. Firstly, the skilled person would not consider D4 for combination with D2 since, as also argued by the respondent, D4 is directed to addressing problems relating to blades having a large fillet (see e.g. paragraphs [0001], [0003] and [0037]). However, even if this incompatibility between D2 and D4 were to be ignored, the off-setting of the cooling passages 28 in D4 to the pressure side of the airfoil would not be an obvious modification to make to the cooling passages 42 in D2 since the direct impingement cooling of the fins 44 would be lost and the cooling airflow in the channel 32 would be completely changed, thus requiring significant redesign of the fins/turbulator/gill holes of D2. In addition, D4 is silent regarding the further differentiating features of claim 1 over D2, namely the angled trip strips on a pressure side of the airfoil or showerhead holes at its leading edge. Thus, even if D2 were to be combined with the technical teaching of D4, the subject-matter of claim 1 would not be reached unless an inventive step were involved.

1.1.9 The appellant's reference to the Coriolis effect disclosed in D4 also applying to D2 is not denied. However, this merely results in the cooling air emitted from the cooling passages 28 of D4 being directed towards the pressure side of the airfoil which, if applied in D2 would still not guide the skilled person to providing the claimed angled trip strips and showerhead holes.

1.1.10 The appellant's argument that angled trip strips offered no surprising cooling effect and so could not provide the basis for an inventive step to be recognised is accepted as far as this argument goes. However, the cooling air flow in D2 is of a very specific nature, air first impinging on the fins 44 before passing over the turbulators and then exiting via the gill holes. Introducing angled trip strips into the channel 32 of D2 would be expected to not insignificantly change the cooling air flow, thus putting into question the entire cooling concept envisaged and its efficacy.

1.1.11 This outcome is not changed through the appellant's reference to G-VII, 10.1 of the Guidelines for Examination (which are anyway not binding on the Board), in which an arbitrary choice of possible features could not justify the presence of an inventive step being recognised. Even if the technical effect of the angled trip strips in isolation were well known, and the selection of these (rather than for example bumps or pins) were arbitrary, the inclusion of the angled trip strips in D2 was not a simple addition with a known technical effect due to the resultant impact of this change on the fundamental cooling air flow in the airfoil of D2.

1.1.12 The appellant's further reference to E1 to prove that angled trip strips were well known is accepted; they indeed are known to the skilled person and this was not denied by the respondent. Nonetheless, as held above, their introduction into the cooling structure disclosed in D2 would not be obvious to the skilled person.

1.1.13 In summary, therefore, when starting from D2 and wishing to solve the posed objective technical problem, D4 would not guide the skilled person to the subject-matter of claim 1 without their exercising an inventive step.

1.2 D5 in combination with the technical teaching of D9

1.2.1 D5 discloses the following features of claim 1:

A cooled airfoil (12) within a gas turbine engine (see col. 1, lines 6 to 8) comprising:

a rib (span rib, 71) which at least partially defines a forward cavity (41) within an airfoil (12), said forward cavity (41) in communication with a cooling circuit flow path (36); and

at least one opening (74) through said rib (71), wherein said at least one opening (74) communicates with a leading edge cavity (leading edge cooling plenum, 70) adjacent said forward cavity (41);

a multiple of showerhead holes (44) within a leading edge (20) of said leading edge cavity (70).

1.2.2 It was undisputed by the parties that D5 fails to disclose:

- said at least one opening offset within said forward cavity relative a longitudinal axis of said airfoil;

- a multiple of turbulators within said leading edge cavity, said at least one opening adjacent said multiple of turbulators;

- wherein said turbulators are defined on the inner wall of said leading edge cavity;

- wherein said multiple of turbulators are angled trip strips defined along a pressure side of the cooled airfoil; and

- wherein said multiple of turbulators are opposite a multiple of gill holes.

1.2.3 The objective technical problem to be solved can thus be seen as being 'how to improve the cooling efficiency in the leading edge cavity of the airfoil of D5'. Both parties accepted this as the problem to be solved.

1.2.4 The technical teaching of D9 does not lead the skilled person to the claimed subject-matter without becoming inventively active. Firstly, D9 is directed to cooling in the trailing edge cavity of an airfoil and so would not be consulted by the skilled person for a teaching relating to the leading edge cavity of D5. Even if it were to be considered, D9 fails to disclose an offset of the inlet hole 42 to the trailing edge cavity, rather the hole is angled towards the turbulators 46 (see paragraph [0038]). Thus, even if the teaching of D9 were to be applied to the leading edge cavity of D5, the claimed offset of the opening relative to the longitudinal axis would not be realised. D9 also fails to disclose turbulators in relation to the leading edge cavity of the airfoil, the entire disclosure of D9 being directed to cooling in the region of the trailing edge cavity.

1.2.5 The appellant's argument that Fig. 3 of D9 showed the inlet hole 42 being offset towards the pressure side of the airfoil is not accepted. It is not appropriate to infer relative dimensions from a figure if these are not clearly understood to be so intended. There is nothing in D9 to suggest, even if it could be inferred from the depiction in Fig. 3 (which is certainly not unambiguously the case), that an offset of inlet hole 42 relative to the longitudinal axis towards the pressure side of the airfoil is deliberate. Rather as paragraph [0038] discloses, the inlet hole 42 is simply angled towards the pressure side of the airfoil. Therefore, no unambiguous disclosure of an offset of inlet hole 42 towards the pressure surface can be inferred from D9.

1.2.6 The appellant's argument that the turbulators in the vicinity of the trailing edge of D9 (see for example paragraphs [0036] and [0044]) were simply given as an example such that the skilled person would also consider employing these at the leading edge of the airfoil is not accepted. An exemplary disclosure of a feature at the trailing edge of an airfoil does not implicitly disclose the same at the leading edge. Even though it is accepted that cooling at both the trailing and leading edges of an airfoil is important, explicit disclosure at one location as an example cannot result in an implicit disclosure at the other. Such a transfer of teaching from leading to trailing edge can also not be seen as routine adaptation for the skilled person. As remarked by the respondent, paragraph [0029] of D9 discloses that the other aerofoil cavities shown in the Figures (which are there to provide cooling) were not the subject of the invention in D9, such that the author of D9 also gave no indication of the immediate relevance of the trailing edge structure to that of the leading edge.

1.2.7 The appellant's argument that the requirement for cooling exists at both the leading and the trailing edges and that the same features enabling this would thus implicitly be used in both locations is not accepted. It is true that a cooling requirement exists at both edges, but the way in which this is achieved in cavities, the cross-section of which are of different shape and size, is not necessarily the same in all instances. There is thus no direct inference possible from D9 that the presence of turbulators in the vicinity of the trailing edge would implicitly result in turbulators being seen as appropriate for cooling the leading edge cavity.

1.2.8 The appellant's further reference to E2 to E5 as having been filed to counter the opposition division statement that the skilled person would be reluctant to make modifications to airfoil cooling channel geometry and components is irrelevant to whether the skilled person would find a teaching in D9 as to how to modify D5. Indeed, there is no such teaching in D9 to guide the skilled person to any modification of the leading edge cavity, let alone to the particular arrangement of offset cooling air opening directing air onto angled trip strips on the pressure side of the airfoil.

1.2.9 In conclusion, therefore, when starting from D5 and wishing to solve the posed objective technical problem, D9 would not guide the skilled person to the subject-matter of claim 1 without their exercising an inventive step.