by Reinhardt Schuster and Clemens Rübel

I. Introduction

In a landmark decision (Chimney Pipe Case), rendered on March 22, 2001, the District Court Düsseldorf, statistically the most frequented first instance Court for patent infringement proceedings in Germany and even in Europe, had to decide on the scope of protection of a patent which limited its scope by numbers in its claims. Here, the Court had to balance important principles against each other when deciding whether the scope of protection also covers embodiments which lie outside of the range indicated by these numbers: The principle of rewarding the inventor with an adequate scope of protection versus certainty of the law in view of the specific claim language. This area of conflict regularly comes up with decisions in the field of the doctrine of equivalents.

II. The doctrine of equivalents

1. The Principle of rewarding the inventor versus certainty of the law

The entire patent law is based on the economic policy consideration that the inventor should be rewarded for his contribution to technical progress by granting a patent and protecting his invention during the (limited) time of the term of his patent. It should be worthwhile for the inventor to disclose as quickly as possible his invention to the public, instead of using it secretly on his own, or leaving the patent unused. In form of a monopoly lasting for a certain period of time, the inventor obtains the economic value of his invention. The scope of this monopoly, however, has to be determined precisely, because competitors have to know the borderline which limits their right to manufacture without entering into conflicts with patents, and from where on they have to ask the inventor for a license or develop and use alternative technologies. The certainty of the law, on the other hand, is as important for the functioning of the economy as the rewarding of the inventor. A precise borderline, limiting the scope of protection, is therefore desirable.

Thus, a limitation of the patent protection to the wording as literally claimed would be very desirable in accordance with the spirit of the certainty of the law. However, it would be easy to circumvent the wording of the patents by changing infringing embodiments in such a way that the embodiment would differ only slightly from the wording of the claims without giving up the principles and advantages of the invention, so that the holder of the patent would not receive his fair reward. The inventor, on the other hand, would like to have everything protected which was published by the patent, including the description and drawings.

2. Applicable law for the scope of protection

The European Patent Law and the literally corresponding German Law try to find a harmonizing compromise in providing that "the extent of the protection conferred by a (European) patent or a (European) patent application shall be determined by the terms of the claims. Nevertheless, the description and drawings shall be used to interpret the claims". The protocol to the interpretation of Art. 69 EPC which is, according to Art. 164 (1) EPC, part of the EPC and applicable to European as well as national patents, again precises the compromise found in Art. 69 EPC:

Art. 69 should not be interpreted in the sense that the extent of the protection conferred by a European patent is to be understood as that defined by the strict, literal meaning of the wording used in the claims, the description and drawings being employed only for the purpose of resolving an ambiguity found in the claims. Neither should it be interpreted in the sense that the claims serve only as a guideline and that the actual protection conferred may extend to what, from a consideration of the description and drawings by a person skilled in the art, the patentee has contemplated. On the contrary, it is to be interpreted as defining a position between these extremes which combines a fair protection for the patentee with a reasonable degree of certainty for third parties.

3. The development of the doctrine of equivalents in case law

The provision that the scope of protection shall be determined by the terms of the claims, does not mean that only the literally claimed embodiments fall within the scope of protection. It is quite impossible to phrase a wording for the claims that includes all conceivable future possibilities. Therefore, criteria have been developed in case law, according to which also equivalent infringing embodiments fall within the scope of protection of the patent. Only such embodiments are protected which use means to an equal effect, which the person skilled in the art would derive from the patent claims by employing the description and drawings on the basis of professional knowledge and of conclusions from the terms of the patent claims. Further, the infringing embodiment has to have an inventive distance to the prior art for being covered by the doctrine of equivalents.

3.1. Equal effect

An objective examination of the equivalent should always start with the question whether the means named in the claims have technically the same effect as the used exchanged means. Hereby, a comparison has to occur between the object of the invention and the attacked embodiment as a whole, not only by comparison of single features, because the technically equal effect can only be considered in view of the scope of the whole solution.

All features should be realized essentially and altogether at least in a different shaping, whereas a feature is given if the concrete embodiment of a feature is to be understood as a form of a general statement, the equal effect of which a person skilled in the art can determine by interpretation. It does not matter whether the concrete accused embodiment has the same number of features as claimed in the asserted patent (see the Fixing Device II Case by the Federal Supreme Court 1994).

3.2 Solving of problem

The equal effect can only be obtained if the problem of the patent can be solved nearly entirely with the exchanged means. The attacked embodiment should have a different teaching than the patent or contradict the basic idea of the invention (Federal Supreme Court 1994: Rake Blade Case).

3.3 The possibility to find the equivalent embodiment

A person skilled in the art must at least be able to deduce the means of the attacked embodiment with equal effect from the claims by employing the description and drawing, based on his professional knowledge (Federal Supreme Court 1994: Segmentation Device Case)By definition of the scope of protection, the whole prior art belongs to professional knowledge, without limitation to the prior art which is cited in the patent specification or which belongs to general professional knowledge. Solutions which are not based on the invention described in the patent claims, but leave the meaning described therein, cannot be judged as an equivalent infringement of the patent. Further, the scope of protection of a patent is also left if an inventive step must be involved to reach the equivalent embodiment.

3.4 The estoppel of the free prior art (Molded Curbstone defense)

In practice, a defendant often tries to defend itself by arguing that the embodiment accused under the doctrine of equivalents does not constitute a patentable invention in comparison to the prior art and therefore does not infringe the patent.

This estoppel was created by a major decision rendered by the Federal Supreme Court in 1986 (Molded Curbstone Case). It was the first decision rendered by the Federal Supreme Court on the basis of the doctrine of equivalents under the new German Patent Act of 1981. Most of the later decisions regarding the doctrine of equivalents refer to this decision. The background of this decision is that the holder of a patent cannot obtain patent protection for something which is not patentable. There is no reason to reward patent protection under the doctrine of equivalents for a solution which is obvious to a person skilled in the art from the prior art. In other words: Anybody is free to use solutions derived from the prior art or suggested by the prior art without involving the asserted invention.

However, the Molded Curbstone Estoppel has its limits: Under German Law, the validity of the patent cannot be challenged in an infringement proceeding. The validity of a patent can only be challenged in a separate opposition proceeding or in a nullity action. Therefore, the defense that the accused product is not patentable in view of the prior art can only be raised, if the prior art cited as support for this argument concerns the modified features of the accused product, and not only those features which literally correspond to the patent. Thus, it is provided that this defense is only applicable in cases of infringement under the doctrine of equivalents and not in cases of literal infringement, in which a separate opposition or nullity case is to be filed for asserting invalidity.

III. Numerical data in the patent claims

In the above mentioned decision of the District Court Düsseldorf concerning the scope of protection of patents which include numerical data in the patent claims, it was to be considered whether an attacked embodiment can fall within the scope of protection of a patent according to the doctrine of equivalents, even if it lies outside the claimed range of numerical data.

In summary, in the Chimney Pipe Case cited above, a chimney pipe made of different pipe parts was claimed with each part having a conically extended and a conically tapered end with an equal cone angle of 0.5° to 2°. The attacked embodiment, however, had a cone angle of about 2.5°. Therefore, a literal use of the patent could not be confirmed, but an infringement according to the doctrine of equivalents could still apply: The accused embodiment has, in the sense of the invention, an equal effect to the patented embodiment and its use was arguably suggested to a person skilled in the art with the knowledge of the claimed range of angles.

Nevertheless, in summary, the Düsseldorf Court argued in the Chimney Pipe Case that the application of the doctrine of equivalents on patents claiming numerical data should be considered differently. Numbers provide only a limited scope for interpretation, as opposed to descriptive or functional claim features. Descriptive indications should be interpreted in order to avoid a lack of clarity in the patent claims, and also for the clarification of the technical terms used in the patent claims as well as for the clarification of the meaning and the significance of the invention. The terms of a concept do not automatically correspond to the wording of the concept. Every patent writes its own dictionary. When the technical features are described in words, the difficulty always arises that they have to be expressed so generally that, at best, all possible embodiments with equal functions are covered and have to be considered in advance. Since this is very difficult and sometimes not possible, the inventor may not receive the reward to which he would actually be entitled and therefore the doctrine of equivalents had been developed.

The possibilities of interpretation, for numerical data and ranges are much smaller. It is only possible in exceptional cases that the meaning or terms of a number do not correspond to its wording. Normally, a number always has the same meaning. At the most, it can be interpreted as to which chemical, physical or mechanical parameter the numbers refer to or with which method of measurement they should be applied. In very rare cases, a correction of patent claims may be considered, e.g. if there is an evident typological mistake in the numerical data, or if a decimal has been moved or the order of numbers has been twisted, provided that a person skilled in the art, after comparison with the specification, detects such an obvious mistake.

There is some more room for interpretation if the numbers are provided with the addition "circa" or "approximately". Here, it is clear that this only concerns the order of magnitude of the corresponding parameters.

It is already clarified by case law that in closed numerical data for a range ("from ... to..."), all single values between the limiting values are covered, even if a single value between the limiting values has special, unpredicted or very ordinary, expected effects. For data with ranges that are open on one side, the interpretation is more difficult. With the patent specification and from the point of view of a person skilled in the art, it has to be determined if, for example, the detail "at least 10" is claimed, whether this patent also covers a value of over 100. It is similarly questionable in case "less than 10" is claimed whether the value "0" is covered by this numerical data.

When formulating a patent, it is much easier to determine a numerical range in which the inventive effect and advantages are given, in comparison to patents in which the inventive effects have to be expressed by words. One can expect from the applicant to make up his mind about the numerical range needed for the purposes of the invention and to compose the wording of the claims and the description in such a way that these maximum and/or minimum values appear in the patent claims, delimiting it from the prior art and representing the content of the invention in the best possible manner.

A very limited application of the doctrine of equivalents for features with numerical data is also required with regard to the certainty of the law. Any third person who has potentially spent a lot of time and money on the development and marketing of products should know exactly the limit between infringement and non-infringement of a patent. As far as claims including numerical data are concerned, a third person can assume that the range was chosen on purpose and that one can go very close to the limit when developing new products. If the judges at infringement courts would create a big "security range" around the precisely claimed range in favor of the holder of the patent, the responsibility for the accurate determination of the claimed protection by the patent would be moved from the holder of the patent to the competitors and the public. Why should a competitor be obliged to judge on his own risk and his own responsibility, when - instead of the numerical limits set by the patentee in the patent claims - the limit is between infringement and non-infringement of the patents? On the contrary, any third person should be able to reliably see the difference between actions that are allowed or not allowed.

On this basis, the court held in the above cited Chimney Pipe Case that, at best, only a very slight divergence from the claims can still fall within the scope of protection according to the doctrine of equivalents, but not a divergence which amounts to approximately 35 %, as in the present case. By indicating the claimed numerical data, the owner of the patent-in-suit consciously wanted to distinguish it from the prior art. Therefore, it was also the patentee's clear intention that ranges outside of the claimed range should remain free. Third persons should be able to rely on the claimed ranges.

IV. Conclusion

If numbers are indicated in the claims, the concept of certainty of the law prevails over the interest in rewarding the inventor, in case the inventor and his agent precise their patent by indicating numbers, and the attacked embodiment lies outside of that value, even if the attacked embodiment would normally infringe according to the doctrine of equivalents.

Therefore, it is advisable to check in detail, before inserting numeric data into patent claims, whether this is really inevitable or whether ranges outside of the indicated range really do not lead to a useful embodiment of the invention. In practice, it is often the case (and the present Chimney Pipe Case is just one example for many) that patents with numeric data are circumvented by embodiments with equal effects and derivable from the claimed data by a person skilled in the art and having slightly different values than the values claimed. At patent infringement courts, the holder of a patent limiting himself in such a way will have limited success in prohibiting such circumventing embodiments.

© by Reinhardt Schuster and Clemens Rübel 2002, attorneys at law with the intellectual property law firm Bardehle Pagenberg Dost Altenburg Geissler Isenbruck, Munich. First published in Managing Intellectual Property, Patent Yearbook, London, 2002.

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