The wording of the claims here includes imprecise and inconsistent term usage, making them difficult to follow and easy to misconstrue under the normal canons of claim construction. While the intended meaning may shine through in parts (including the dependent claims), this is not enough to save the independent claims from their ordinary meaning. As the court concluded, “[e]ven if there is an error in drafting, the claims as drafted are what the patentee claimed and what the public is entitled to rely on.”
Background / Facts: The patents here describe internal combustion engines controlled to “precisely regulate[] the fuel/air mixture for combustion and exhaust emission control.” In the disclosed systems, fuel is injected in first and second fractions at different points in the operating cycle of the engine, resulting in a combustion process having “a constant volume (isochoric) phase and a constant temperature (isothermal) phase.” The limitation at issue is in independent claim 1, which recites that “the combustion as a result of the introduction of the second fraction is a substantially isothermal process.” Despite the equivalence language that “the combustion … is a substantially isothermal process,” the patentee asserts that this does not require that “the combustion” as a whole be isothermal “from the beginning until the end of that combustion” as interpreted by the district court, noting that dependent claim 4 calls for the second fraction combustion to be divided into two portions, of which only the second is isothermal.
Issue(s): Whether by virtue of the doctrine of claim differentiation the limitation added in dependent claim 4 indicates that the interpretation of independent claim 1 cannot exclude that limitation.
Holding(s): No. “The only permissible reading of the limitation ‘the combustion … is a substantially isothermal process,’ … is that it requires a substantially constant temperature for the entire second fraction combustion. ‘[I]s’ ties the subject (‘the combustion’) to the following description (‘a substantially isothermal process’). The subject is introduced with the definite article (‘the’), indicating a particular combustion, i.e., the combustion of the second fraction. ‘[T]he combustion … is a substantially isothermal process,’ does not indicate that only a portion of the combustion is isothermal; instead, it indicates that the entire combustion is isothermal.” The doctrine of claim differentiation creates only a presumption of consistency among the claims, but “the presumption will be overcome where the ordinary meaning of the words in an independent claim do not admit to a construction that would embrace a claim dependent therefrom.” The court emphasized that it “will not redraft claim 1 contrary to its ordinary meaning to avoid a conflict with claim 4.”