Interpretative Spotlight: “Gradually”

This is an appeal against a refusal of an application.

The single claim according to the request submitted during the oral proceedings (OPs) before the Board read as follows:

1. A gas turbine engine comprising a plurality of blades, each blade comprising:

a platform (52);

a shank (54) extending from the platform;

a dovetail (56) extending between an end (101) of the blade and said shank for mounting said blade within the gas turbine engine, said dovetail comprising at least one tang (86);

an airfoil (50) comprising a first sidewall (60) and a second sidewall (62) extending in radial span between said platform and a blade tip (70); and, a cooling cavity (102) in the blade that extends through the airfoil, the platform, the shank, and the dovetail, wherein the portion of the cavity defined within the dovetail includes a root passage section (120) having a first width (DR), and a transition passage section (122) that extends between the root passage section and the portion (114) of the cavity defined within the shank, and wherein the portion of the cavity defined within the shank has a second width (DS) that is larger than the root passage section first width (DR); wherein the root passage section first width (DR) is substantially constant within the root passage section (120) and the transition passage section (122) is tapered between the root passage section and the portion (114) of the cavity defined within the shank (54), such that the width of the transition passage section (DT) tapers outwardly between the root passage section and the shank portion; and

a coating on the inner surface (104) of the blade that defines the cooling cavity, the coating being an oxidation resistant environmental coating (105), characterized in that

at least a portion of said cooling cavity has a coating having a thickness greater than 0.0254 mm (0.001 inches), and in that

the inner surface (104) of the cooling cavity (102) is defined with an arcuate interface (156) having a predefined radius between the transition passage section (122) and the root passage section (120) of the cavity, wherein the combination of transition passage section length (146) and the arcuate interface (156) enables the transition passage section (122) to taper gradually outward between the root passage section (120) and the shank portion (114), and with an arcuate interface (170) between the transition portion (122) and the shank portion (114) of the cavity, and wherein the transition passage length (146) enables the arcuate interface (170) to be defined between the transition passage section (122) and the shank portion (114). (my emphasis)

The Board found this claim to lack clarity:

[1] Claim 1 of the sole request submitted during the OPs does not meet the requirements of Article 84 EPC 1973. In particular, the feature “wherein the combination of transition passage section length (146) and the arcuate interface (156) enables the transition passage section (122) to taper gradually outward between the root passage section (120) and the shank portion (114)” lacks clarity.

[1.1] This feature has been taken almost literally from page 7 of the description of the only preferred embodiment of the invention, illustrated in Figure 3. The relative term “gradually”, which has no well-defined meaning in the art, is not further defined in the description of in this embodiment. Its meaning can be understood however in comparison to the abrupt transition between the corresponding sections in the blade of the prior art shown in Figure 5.

[1.2] The appellant’s construction of the feature “taper gradually outward” relies on a comparison of the taper angles of the transition passage section in a blade of the preferred embodiment of the invention (Fig. 3) with an angle of the corresponding section in a prior art blade (Fig. 5). In these two blades, the respective diameters of the adjacent root passage section DR, and the shank portion DS, are shown to be essentially unchanged. The length of the transition passage section is altered and the sharp corners at both ends of the transition passage section of the prior art blade are replaced by arcuate interfaces in the blade according to the embodiment of the invention. By comparing the two blades of these Figures indeed the outwardly tapering transition passage section of the preferred embodiment of the invention is longer and therefore, by joining at their ends the respective root passage section and shank portion, leads to a less abrupt or more shallow taper angle compared to that in Figure 5. However, the subject-matter of the claim does not refer to any prior art blade, so that the feature “taper gradually outward” remains vague and without precise meaning.

[1.3] Even if it were assumed that the skilled person would, from the present wording of the claim, understand the feature “to taper gradually outward” in the sense of a more shallow taper angle compared to the prior art disclosed specifically in Figure 5, it would remain entirely unclear where the limit lies, for example in terms of degrees of an angle, between an abrupt transition, of the prior art, and a gradual transition as intended by the claimed subject-matter. The application does not disclose any absolute or relative dimensions of the geometry of the cooling cavities’ various sections for the blade according to the embodiment of the invention or the prior art blade. The appellant was also unable to provide any indication where such a limit between the prior art and the claimed subject-matter should be drawn, nor could the Board itself determine any disclosure in the application which would clarify this. The comparison of the length of the transition passage sections and consequently the meaning to be given to the feature “taper gradually outward” relies thus on unspecified dimensional relationships of a non-standardised prior art blade having a particular cooling cavity geometry with an allegedly abrupt transition. The feature consequently does not allow a skilled person to understand with any clarity what is meant by this feature of the claim.

[2] According to Article 12(2) RPBA the grounds of appeal shall contain a party’s complete case. Article 13(1) RPBA sets out that any amendment to the party’s case may be admitted and considered at the Board’s discretion. The discretion shall be exercised in view of the complexity of the new subject-matter submitted, the current state of the proceedings and the need for procedural economy. In order to be in line with the requirement of procedural economy, a request filed at a late stage of the procedure should be prima facie allowable in the sense that it overcomes the objections raised against previous requests and does not introduce new objections.

Since the claim of the sole request submitted during the OPs does not meet the requirement of A 84 EPC 1973, this request is not prima facie allowable in the aforementioned sense. It was thus not admitted into the proceedings.

[3] Since the only request on file was not admitted, the appeal could not be allowed since there was no request in proceedings upon which grant of a patent could be based. […]

The appeal is dismissed.

Should you wish to download the whole decision (T 1075/10), just click here.

The file wrapper can be found here.