According to claim 1 of the patent in suit, these passages for hot combustion gases are provided over the entire length of the combustion chamber.
The defendant had been sentenced for an infringement in earlier proceedings and then came up with a modified version of the boiler were some of the passages in the metallic heat exchanger body were closed with some sort of plastic matter. As a result, only 85 % of the lengths of the combustion chamber were provided with (open) passages and the rest was clogged.
The plaintiff argued that the passages would still exist despite of being clogged by plastics and that the plastics would degraded and burned after a while such that the passages would be open. Export evidence on the last point was contradictory such that the court concluded that the allegedly infringing product as it was presented did not show passages provided over the entire length of the combustion chamber. Once the passages are clogged, they do no longer qualify as passages in the sense of the patent.
Turning to infringement by equivalent means, the board re-emphasizes that the finding of equivalence requires that the considerations of the skilled person are oriented on the technical teaching of the claim and that the claim is not only the starting point but rather the essential basis for the consideration of the person skilled in the art (BGH Pumpeneinrichtung). At the same time, the patentee is limited to the technical teaching he has requested to be protected (BGH Kunststoffurteil). According to the court, the technical teaching given by the patent has to be accepted by the person skilled in the art as sensible and must not be questioned in its technical justification when searching for an equivalent means as a replacement of a feature in the claim.
In the case at issue, the claim teaches that the cylindrical surface of the heat exchanger provided for exchanging heat can be and should be used in its entirety. Accordingly, the required uniform heat transmission onto the heat exchanger can be achieved only when the passages are provided over the entire length of the surface of the heat exchanger which separates the combustion chamber from the exhaust gas chamber.
Consequently, the allegedly infringing embodiment was found not to infringe the patent by equivalent means.
The German Text of the Judgement can be found here.