The Doctrine of Equivalents in U. S. Patent Law

This is a comment on the case Warner Jenkinson Co., Inc. v. Hilton Davis Chemical Co. decided by U. S. Supreme Court on March 3, 1997, 117 S. Ct. 1040 (US 1997), which deals with the doctrine of equivalents, or the infringement under the doctrine of equivalents.

In the United States, the doctrine of equivalents is not a statutory provision in the patent law, but a set of rules established by a series of cases when courts decide infringement of patent. The modern doctrine of equivalents in the United States was set out by the Supreme Court case Graver Tank & Mfg. Co. v. Linder Air Products Co., 339 U. S. 605 (1950). One passage often quoted in the case is read as follows:

What constitutes of equivalency must be determined against the context of the patent, the prior art, and the particular circumstances of the case. Equivalence, in the patent law, is not the prisoner of a formula and is not an absolute to be considered in a vacuum. It does not require complete identity for every purpose and in every respect. In determining equivalents, things equal to the same thing may not be equal to each other and, by the same token, things for most purposes different may sometimes be equivalents. Consideration must be given to the purpose for which an ingredient is used in a patent, the equalities it has when combined with the other ingredients, and the function which it is intended to perform. An important factor is whether persons reasonably skilled in the art would have known of the interchangeability of an ingredient not contained in the patent with one that was.

After Graver Tank, U. S. Supreme Court had not decided any case relating to the doctrine of equivalents in almost 50 years. In that period, the inferior courts gradually diverged from their opinions in applying the doctrine of equivalents, whereas intense debates were occurred among judges, patent attorneys, and professors. Therefore, the Supreme Court restated some basic elements concerning the doctrine of equivalents in Hilton Davis, and cleared many issues relating to the debates.

2."Element by Element" Test

How to interpret a patent claim is a key issue in deciding whether an infringement of the patent occurred there. When the Federal Circuit decided Hilton Davis Chemical Co., v. Warner Jenkinson Co., 62 F. 3d 1512, (Fed. Cir. 1995), it used "insubstantial difference" test to decide whether the accused product or process infringed the patented product or process. That is, if the accused product or process as a whole is the same one as the product or process covered by the patent, there is an infringement under the doctrine of equivalents, otherwise there is no infringement under the doctrine of equivalents. However, this is more close to the central claiming principle in interpretation of a patent claim, which is contrary to the peripheral claiming principle used by U. S. courts for a long period.

In Hilton Davis, the Supreme Court struck down the insubstantial difference test and affirmed the element by element test put forward by Judge Nies of Federal Circuit in a dissenting opinion. The Supreme Court stated:

Each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole. It is important to ensure that the application of the doctrine, even as to an individual element, is not allowed such broad play as to effectively eliminate that element in its entirety.

This is the element by element test and the typical peripheral claiming principle. The Supreme Court said confidently that "So long as the doctrine of equivalents does not encroach beyond the limits just described, or beyond related limits to be discussed infra, we are confident that the doctrine will not vitiate the central functions of the patent claims themselves."

In deciding Hilton Davis Chemical Co. v. Warner Jenkinson Co., the Federal Circuit and the parties argued whether the "function-way-result" test is a suitable method for determining equivalence, or whether the "insubstantial differences" approach is better. The Supreme Court stated that those linguistic frameworks are less important than "element by element" test in applying the doctrine of equivalents. "An analysis of the role played by each element in the context of the specific patent claim will thus inform the inquiry as to whether a substitute element matches the function, way, and result of the claimed elements, or whether the substitute element plays a role substantially different from the claimed element." Therefore, the Supreme Court has the "insubstantial difference" and "function-way-result" as methods or approaches within the "element by element" test in determining equivalence, rather than the ones that are independent of, or substitute of "element by element" test.

3.Prosecution History Estoppel

Prosecution history estoppel is a legal limit to the doctrine of equivalents to the effect that any surrender of subject matter during patent prosecution to avoid the prior art may not be recovered by the patent owner later, even if it is equivalent to the matter expressly claimed.

Prosecution history estoppel is closely connected to the procedure of patent examination. In this case, although Hilton Davis Chemical Co. filed an application with no limit on the pH in its patent claim, it narrowed the pH levels between 6.0 and 9.0 in responding to the requirement by the patent examiner. To add the upper limit of 9.0 is to distinguish a prior patent, whereas the reason for adding the lower limit of 6.0 is unclear.

Because the process of Warner Jekinson Co. has a pH of 5.0, it argued that Hilton Davis Chemical might not recover any subject matter it surrendered during the patent prosecution, regardless of the reason for such surrender. The Supreme Court believed that, however, Warner Jekinson Co. "reaches too far in arguing that the reason for an amendment during patent prosecution is irrelevant to any subsequent estoppel. In each of our cases cited by petitioner and by the dissent below, prosecution history estoppel was tied to amendment made to avoid the prior art, or otherwise to address a specific concern--such as obviousness--that arguably would have rendered the claimed subject matter unpatentable." Thus only may the subject matter surrendered in the prosecution to avoid the prior art not be recaptured by applying the doctrine of equivalents.

In this respect, the reason for surrendering any subject matter in the prosecution is very important. The Patent Office may request an amendment of a claim for various reasons, but "certain reasons for a claim amendment may avoid the application of prosecution history estoppel is not tantamount to holding that the absence of a reason for an amendment may similarly avoid such an estoppel." Because the reason for Hilton Davis to add a lower pH limit of 6.0 is not clear, the Supreme Court remanded the case to the Federal Circuit.

4.The Proper Time for Evaluating Equivalency

A patent claim has two functions: defining an invention and providing a public notice. Warner Jekinson Co. argued in petition that in order to minimize conflict with the notice function of patent claims, the doctrine of equivalents should be limited to equivalents that are disclosed within the patent itself. This means that the proper time for evaluating equivalency is the time of application or the time when a claim is finalized. A milder argument by dissenters in Federal Circuit is that the doctrine should be limited to equivalents that were known at the time the patent issued.

The Supreme Court hold that "insofar as the question under the doctrine of equivalents is whether an accused element is equivalent to a claimed element, the proper time for evaluating equivalency-and thus knowledge of interchangeability between elements-is at the time of infringement, not at the time the patent was issued."

This time point for evaluating equivalency is very important to patent owner. In the patent examination, the patent office may ask the applicant to exclude the element from the claim that is equivalent to or obvious to a prior art and thus set the scope of the patent. From that time on, other persons may improve the invention further along with the development of specific technology. If the improvement is a nonobvious one, it is a new invention and may get a new patent. If it is an obvious one, it is still within the scope of the original patent and is protected by applying the doctrine of equivalents. Apparently if the time for evaluating equivalency is the time of application or issuing patent, the patent owner may not get that kind protection, and the purpose of the patent law to protect invention and encourage invention will be jeopardized.

5.The Intent of the Alleged Infringer

Warner Jekinson Co. developed its process independently and did not learn the patent owned by Hilton Davis Co. until it begun commercial use of its process. Thus Warner Jekinson Co. argued in petition that the intent of the alleged infringer should be explored before the application of the doctrine of equivalents.

Graver Tank did leave room for the inclusion of intent in applying the doctrine of equivalents, such as referring to the problem of an "unscrupulous copyist" and "piracy". In Addressing to this, Federal Circuit distinguished copying, designing around a patent, and independent experimentation. In disagreeing with this, the Supreme Court stated: "This explanation leaves much to be desired. At a minimum, one wonders how ever to distinguish between the intentional copyist making minor changes to lower the risk of legal action, and the incremental innovator designing around the claims, yet seeking to capture as much as is permissible of the patented advance."

The Supreme Court believed that the better way is whether there is a "known interchangeability" between the patented element and the accused element in the eye of one skilled in the art. If it is, or the accused one is a substitute of the patented one, an infringement exists; if it is not, or the accused one is not a substitute, an infringement does not exist. Because this method has no relationship with the subjective condition of the alleged infringer, it is an objective method in applying the doctrine of equivalents.

The Supreme Court concludes that "Although Grave Tank certainly leaves room for petitioner's suggested inclusion of intent based elements in the doctrine of equivalents, we do not read it as requiring them. The better view, and the one consistent with Graver Tank's predecessors and the objective approach to infringement, is that intent plays no role in the application of the doctrine of equivalents."

6.Conclusion

This paper is intended to introduce the doctrine of equivalents in U. S. patent law into Chinese legal circle. Although many Chinese scholars have explored the doctrine of equivalents, and many Chinese Judges have applied the doctrine of equivalents to decide cases, those are preliminary explorations and tentative applications. In this respect, Hilton Davis discussed many issues in a deep going way concerning the doctrine of equivalents, and is worth of Chinese scholars and judges to take reference from it. It is hoped that this paper will further the understanding of the doctrine of the equivalents by Chinese scholars and judges and thus improve the research and the judiciary.