T 2108/21 Plausibility in mechanical inventions

Disclaimer: the author of this article was actively involved in the case discussed below.

The most discussed EPO decision of 2023 - when ignoring the never-ending saga of pre-grant description amendments - certainly was the decision of the Enlarged Board of Appeal in G 2/21. The opposition case leading to this decision concerned a patent on a group of compounds that can be used as an insecticide composition. In the European patent law community, this case is often referred to as "the plausibility case". The main dispute between the two parties in that case (Sumitomo and Syngenta) centred on the question of whether the claimed invention involved an inventive step and what evidence can be used in EPO examination and opposition proceedings to prove or disprove the presence of an inventive step.

Plausibility

The questions that needed to be answered by the Enlarged Board in G 2/21 concerned how plausible an alleged technical effect needs to be to allow an applicant or proprietor to submit inventive-step-supporting evidence after the initial filing date of the patent application. The Enlarged Board skilfully side-stepped most of the plausibility discussion and reverted to the established legal principle that "any effect provided by the invention may be used as a basis for the reformulation of the technical problem, as long as said effect is derivable from the application as filed (see?T?386/89)" (GL G-VII 5.2). Or in the words of the Enlarged Board (Headnote 2/Reason 94):

A patent applicant or proprietor may rely upon a technical effect for inventive step if the skilled person, having the common general knowledge in mind, and based on the application as originally filed, would derive said effect as being encompassed by the technical teaching and embodied by the same originally disclosed invention.

Of course, for determining whether the skilled person would consider an effect to be encompassed by the original technical teaching it remains important to consider the plausibility of an alleged technical effect. It's easy to write down that a new compound cures all cancers, but without any supporting data, such a claim is not very plausible.

The relevance of plausibility in different technical fields

The plausibility of an alleged inventive step and the use of evidence to (dis)prove the presence thereof has traditionally been more common in technical fields like biotech and pharmaceutics. Just from the well-defined structure of a new compound, it can be very difficult (if not impossible) to predict its technical properties.

Recently, there has been some discussion too (e.g., here, here and here) about the use of experimental data as evidence for the presence of an inventive step in inventions based on the use of artificial intelligence for the processing of technical data.

In the context of purely mechanical inventions, the use of experimental data is often considered far less important. The technical effects of mechanical inventions are normally entirely predictable for any skilled person who understands the basic principles of classical physics. However, in T 2108/21, the recent Board of Appeal decision I am going to discuss now, the plausibility of an alleged technical effect played an important, even decisive, role in the eventual revocation of the patent.

The patent: rotor blade winglets

The disputed patent claimed a new winglet (aka wingtip device) for a rotor blade of a wind turbine. The winglet can be defined by a plurality of design parameters (sweep, pre-bend, chord, spanwise radius, twist angle, and cant angle). The main embodiment described in the patent used specific values for all of those parameters and the description stated that "it has been found that the disclosed winglet may generally improve the overall performance and efficiency of a wind turbine".

To not just protect exact copies of this winglet, the applicant converted the winglet dimensions from mm to % of blade span, added tolerance ranges to all parameters, and selected a subset of the parameters for claim 1. In examination, the applicant added another one of the parameters to claim 1 in order to overcome a novelty objection of the examiner.

In opposition, new prior art was cited and granted claim 1 was decided not to be novel. In response thereto, the proprietor decided to restore the novelty of claim 1 by narrowing down the tolerance ranges of two of the initially claimed parameters. The proprietor then successfully defended the inventive step of this novel claim by referring to the above-mentioned improved overall performance and efficiency, and the fact that none of the cited prior art documents provides the skilled person with a clear incentive to use the now claimed combination of design parameters.

The appeal

The opponent did not agree with the findings of the opposition division and filed an appeal. In this appeal, the proprietor defended the uniqueness of the claimed winglet and its resulting improved performance with a reference to the Case Law Book (Chapter III.G.5.1.2b):

In T?862/11 the appellant (opponent) failed to submit comparative tests in support of its own assertion that an improvement was implausible owing to the lack of any evidence. […] The problem stated in a granted patent is deemed to have been plausibly solved by the claimed invention when there are no grounds to suspect otherwise. […] The opponent bears the burden of proving its assertion or must at least furnish evidence liable to raise doubts that the problem has indeed been solved (T?534/13, citing T?1797/09, point?2.7 of the Reasons).

The opponent, and the Board, did not agree and argued that in the absence of a plausible technical effect derivable from the original patent application, it is up to the proprietor to show why the claimed invention solves a technical problem of the closest prior art. In the words of the Board (emphasis added):

Thus, the patent provides no data or comparative tests whatsoever that might link any specific one of the various design parameters […] to the very broadly defined effect of improved efficiency and performance. It is the Board's view, see also Chapter I.D.4.3.1, CLBA 2022, that, given that the claimed invention resides in specific ranges of values of specific design parameters, and unless this is not already apparent from common general knowledge, the patent must demonstrate either by a cogent explanation or by comparative test data that those specific value ranges are plausibly linked to alleged effects. […] As both an explanation and data are missing any link between claimed parameter ranges and effect has not been plausibly demonstrated and thus the burden of proof shifts to the appellant proprietor.

This lack of plausible explanation of a specific technical effect for the claimed design parameters then reduced the objective technical problem to nothing more than providing a rotor blade with a different design or geometry. The claimed winglet was decided to be nothing more than an obvious alternative to the already known winglets.

Interestingly, the Board followed the same line of reasoning for all auxiliary requests, including one wherein the claim was narrowed to the exact same embodiment as described in the description. So, even an explicit link between the claimed combination of features and the alleged technical effects was not deemed sufficient, because this link was not backed up by a plausible explanation.

Take-away points

Even though this case concerns a purely mechanical invention, it is important to note that the way in which the claims defined the invention was of a more 'chemical' nature. The use of combinations of parameter ranges is more common to the fields of chemistry and pharmaceutics than to the field of physics and mechanics. Nevertheless, in this case, the Board of Appeal made it very clear that the plausibility of an alleged technical effect is an essential requirement for patents in all fields of technology. When the benefits of an invention can not easily be proven by mere explanation based on established laws of physics, it is not enough to just state that the claimed combination of features provides some improvement over the prior art. Comparative test data and well-described simulations may be used to show why the claimed invention is worth a granted European patent.