It is a well-known principle of U.S. patent practice that an “applicant is entitled to be his or her own lexicographer and may rebut the presumption that claim terms are to be given their ordinary and customary meaning by clearly setting forth a definition of the term that is different from its ordinary and customary meaning(s).” (M.P.E.P. 2111.01, paragraph IV).
The EPO also accepts this principle to some extent, although Examiners nowadays often require such definitions to be inserted into the claims.
What I found interesting in the present decision is that it transfers the lexicography principle to prior art (patent) documents.
The appeal was filed by the patent proprietor after its patent had been revoked by the Opposition Division.
In what follows, the Board discusses the patentability of the main request claim 1 of which read (in English translation):
 Compressed air processing apparatus (CAPA), comprising:[1.1] a pressure controller (5);[1.2] an air dryer (6);[1.3] a multi-circuit protection valve (7); and[1.4] an electronic control unit (40) to control[1.4.1] the pressure controller,[1.4.2] the air dryer[1.4.3] and the multi-circuit protection valve,characterised in that[1.5] the electronic control unit (40) of the CAPA is also designed to control valves (10) of an air suspension system, and in that[1.6] a switching valve (52) that supplies compressed air to the air suspension system or de-aerates the air suspension system, respectively, is arranged in the CAPA. (marginal references proposed by the appellant and accepted by the Board)
*** Translation of the German original ***
[2.1] It is undisputed that D1 discloses a CAPA according to claim 1 of the main request, with the exception of the following features: pressure controller (feature [1.1]), multi-circuit protection valve (feature [1.3]) and the characterising feature (feature [1.6]).
[2.2] Regarding feature [1.6], the appellant has submitted that the CAPA according to D1 only disclosed valves for supplying [compressed air] to the air suspension system and that only such valves (as opposed to de-aerating valves) were provided in this apparatus.
[2.3] The Board cannot accept this argument because it contradicts the disclosure of document D1. The introduction of the description of document D1 […], where the state of the art is acknowledged,
mentions that it was common until then to arrange the valves used for compressed-air conditioning (Druckluftaufbereitung), and thus for supplying [compressed air] to the air suspension system, in the CAPA (“dispositif de traitement”) […] whereas the electrovalves (“électrovalves”) used for controlling the air suspension system were arranged in the vicinity of the pneumatically suspended axles […]. The inventive idea (erfinderische Gedanke) disclosed all over document D1, according to which the pneumatic suspension system is controlled in a centralised manner in the CAPA, via electrovalves, rather than in specific functional units comprising these electrovalves, which are, for instance, provided in the vicinity of the pneumatically suspended axles […], is quite comparable with the one underlying the impugned patent. According to this teaching the electrovalves that control the suspension air bellows are integrated centrally in the CAPA and not scattered over several places such as in the prior art acknowledged in D1 […]. According to D1, one common electronic control unit 10 for controlling the pneumatic suspension is provided in the CAPA […].
[2.3] Before D1 was published the person skilled in the field of air suspensions was aware (cf. D4) that electrovalves for controlling air bellows of a suspension have to both supply compressed air and de-aerate, e.g. when a certain load-independent difference of heights between the chassis and the pneumatically suspended axles has to be maintained (D1 […]). When compressed air is supplied to the pneumatic air bellows (referred to as “cousins d’air” in D1) then the vehicle body is lifted up against the weight of the vehicle. When the pneumatic air bellows are de-aerated, the vehicle lowers because of its proper weight.
[2.4] The parties agreed that the function of “controlling the air suspension system” includes both supplying air to the bellows of the air suspension system and de-aerating them. It is true indeed that document D1 does not explain in every detail how the idea of centralising is to be reduced to practice. In particular, it does not show how the mentioned electropneumatic components are connected and designed. However, the skilled person encounters no difficulties in practically realising this centralising idea. When the air supply and the de-aerating has to be done via electrovalves, this implicitly requires the electrovalves to be switching valves (Schaltventile). Document D4 shows in detail how such valves operate.
[2.5] The [patent proprietor] has based its proper interpretation of D1 on the absence of a detailed description of the electrovalves and their pneumatic mode of operation as well as on certain passages and figures of D1a [i.e. the German translation of D1]. According to this interpretation, the air bellows mentioned in D1 cannot be directly connected to the outlet of the CAPA but are connected via de-aerating switching valves which it believes to be mentioned as “actuating elements” (“Betätigungselemente”) in D1a and which had to be arranged downstream of the CAPA.
[2.5.1] The Board is of the opinion that this view of things contradicts the teaching of document D1. When interpreting the disclosed state of the art, the Board refers to the original document D1 because there are some inaccuracies due to translation in D1a. For example, the expression “actuating elements” of D1a […] does not exactly correspond to the original expression “actionneurs pneumatiques” […] for which “pneumatic actuators” would be a more correct translation. Apparently “actuators” refers to the actuators of the air suspension system, i.e. the air bellows (also referred to as “cousins d’air” in D1).
[2.5.2] The Boards of appeal of the EPO have explained in several decisions that a patent document may be its own lexicon (see, for instance, T 1321/04 and T 500/01). In accordance with this principle the disputed terms mentioned above have to be assigned the meaning that is found in the description of document D1. In the present case, [the Board] notes, based on the numerous passages of D1 using these terms […] that the expression “sortie d’air destinée à l’alimentation” in D1 is to be understood as a general conduit for “supplying” energy needed for generating displacements (zu Verstellzwecken), wherein the displacement movements as such can be generated both with and without energy supply on behalf of the CAPA, as the case may be. I this context the skilled person understands that the air bellows (“coussins de suspension”) or the actuators (“actionneurs”) can indeed be de-aerated via this conduit (“conduit destine à l’alimentation”), the latter being passive, which means that there is no need for the CAPA to supply pneumatic energy during the de-aeration phase. The amount of air generated during the de-aeration may exhaust via the damped outlet of the CAPA (cf. Figs. 1 and 2 “silencieux d‘échappement 6”). Thus the [patent proprietor’s] interpretation is based on an incorrect interpretation of the terms “alimentation” or “alimenter”, respectively, and “actionneurs”.
[2.5.3] Document D1 uses a unified terminology for disclosing three levels within a control chain, i.e. the electronic unit (“unité de contrôle commande électronique”), the electric control valves (“composants électropneumatiques” or “électrovalves”, respectively), as well as the actuators (“actionneurs” or “coussins de suspension”, respectively), which form the last level of this chain of control. The second paragraph on page 5 of D1 unambiguously discloses that, contrary to the opinion of the [patent proprietor] the CAPA according to D1 has the feature [1.6].
[2.6] As to its assumption that the air-suspension bellows cannot be directly connected to the CAPA of D1, the [patent proprietor] also has referred to valve 27 of Fig. 3 of D1 and submitted that this valve did not comprise a switch position allowing to de-aerate.
In this context it has to be noted that valve 27 of Fig. 3 of D1 is only disclosed as a valve that transmits the air pressure (“pression délivrée par l'intermédiaire d'une électrovalve 27”) […]. This does not exclude that […] the actuator (“actionneur”) supplied by valve 27 may also be de-aerated via the CAPA. Moreover, it should be noted that the valve 27 is only represented by way of example and, according to […] D1, belongs to a module 16 for controlling the hand brake. Fig. 3 of D1 is a simplified functional chart […] and, therefore, cannot be used as evidence for the detailed design and the precise connectability of the pneumatic component.
[2.6.1] Moreover, paragraph  of D1a cited by the [patent proprietor] does not mean that it is necessary for the pressure sources to be within each axle. Rather, this paragraph does not make any statement on where to provide the pressure sources. It only states that the different air bellows of an axle may be supplied by separate pressure sources or via a common pressure source […]. This allows to supply the air bellows of the right and left side of the vehicle separately or jointly. This view is confirmed in another passage […] of D1.
[2.7] It remains to be examined whether features [1.1] and [1.4] are known from D1. However, it is not necessary to dwell on this question because even if the assumption of the [patent proprietor] that these features are not known from D1 is accepted, these features cannot contribute to an inventive step:
[…] D1 explains that the core piece 37 of the disclosed CAPA comprises the electropneumatic organs which are needed for controlling the air pressure supplied by the compressor, for drying the compressed air and for its distribution to the different service brake circuits, and which are known as such. The skilled person knows the design and interaction of these organs, e.g. from document D2 (cf. Fig. 1 of D2: pressure controller 2, air dryer 4, multi-circuit protection valve 3, control electronics 52). This document is cited in the introduction of the description of D1 […]. So the skilled person is clearly instructed to provide the core piece of the CAPA of D1 with a pressure controller, (feature [1.1]) and a multi-circuit protection valve (feature [1.4]) according to D1. When doing so, it is obvious to control the valves of these organs in the known way by means of the existing electronic control unit.
[2.8] Thus the Board comes to the conclusion that the subject-matter of claim 1 is not inventive, for the reasons given above, and, therefore, does not comply with the requirements of A 56 EPC 1973. Thus the ground for opposition pursuant to A 100(a) EPC 1973 hinders [the Board] from maintaining the patent as granted.
I am not sure what to think of this. The lexicon principle makes sense when interpreting claims, which form a unit that is distinct from the description. Does it make sense to apply the principle to prior art documents, where the distinction between claims and description is not really relevant and where the general rules of interpretation apply?
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