Lee International

Since the decision in Supreme Court Case No. 97 Hu 2200, issued on July 28, 2000, it has been established in Korea that even if a product or process include some elements which replace or substitute elements of a patented invention, and thus does not literally infringe the patented invention, infringement under the doctrine of equivalents may be found if the following five conditions are met: (i) the accused product or process uses the same principle to solve the same problem as the patented invention; (ii) despite the substitution, the accused product or process produces substantially the same effect as the patented invention; (iii) the substitution is easily conceivable by a person of ordinary skill in the art; (iv) the accused product or process was not known at the time of filing or could not have been easily conceived from the prior art; and (v) the substitution was not intentionally excluded from the patent claims during prosecution.

In Supreme Court Case No. 2019 Da 237302, issued on March 11, 2021, the Supreme Court rendered a decision making criteria for requirements (i) and (ii) above more concrete.

1. Case History and Issues

In this case, Patentee A holding a patent entitled “Detachable Handle for Cooking Utensil” filed a patent infringement action against Company B. The Patent Court determined that although Company B’s product substituted a claim element of Patentee A’s patented invention, Company B’s product applied the same principle to solve the same problem as the patented invention and produced the same effect as the patented invention, and such substitution was easily conceived by a person having ordinary skill in the art. As such, the Patent Court held that infringement under the doctrine of equivalents exists.
The main issue at the Supreme Court was whether requirements (i) and (ii) above were satisfied for determining infringement under the doctrine of equivalents.

2. Supreme Court’s Determination

With respect to requirement (i), the Supreme Court held that when determining whether the accused product has the same principle to solve the same problem as the patented invention, the core technical idea on which the unique technical solution of the patented invention is based, should be determined in view of the specification of the patented invention and the techniques known at the time of filing, instead of perfunctorily extracting some of the elements in the patent claims.

With respect to requirement (ii), the Supreme Court held that it is necessary to examine that the problem that was unsolved in the prior art but is solved by the patented invention can also be solved by the accused product in order to determine the accused product produces substantially the same effect as the patented invention. Thus, in principle, the accused product is deemed to produce the same effect as the patented invention if the core technical idea of the patented invention is also embodied in the accused product. Further, if the core technical idea was known at the time of filing, such technical idea is not considered unique to the patented invention, and thus, the patented invention cannot be deemed to solve the problem that has not been solved in the prior art. In such case, whether the accused product produces the same effect as the patented invention should be determined by comparing the individual function or roles of the equivalents in the accused product to the claim elements, rather than based on whether the core technical idea of the patented invention is embodied in the accused product.

In this case, the Supreme Court applied the above principle to determine infringement under the doctrine of equivalents. It was determined that the technical ideas relating to the improvement in convenience and safety in operation of a handle according to Patentee A’s invention were disclosed in various prior art references. Thus, whether Company B’s product produces the same effect as Patentee A’s invention cannot be determined based on whether the technical ideas are embodied in Company B’s product, but should be determined by comparing the individual functions and roles of the claim elements to the equivalents in Company B’s product. Upon comparison, the Supreme Court determined that the equivalents do not produce the same effect as the claim elements and the claim elements of Patentee A’s invention cannot be easily substituted with the equivalents in Company B’s product. On this basis, the Supreme Court overturned the Patent Court’s decision of patent infringement.

3. Significance and Implications

The Supreme Court’s decision is significant in providing specific criteria for requirements (i) and (ii) to determine infringement under the doctrine of equivalents. With respect to requirement (i), the Supreme Court clarified that in order to determine whether the accused product has the same principle to solve the same problem as the patented invention, the core technical idea of the patented invention should be clearly identified in view of the specification of the patented invention and the prior art at the time of filing. With respect to requirement (ii), the Supreme Court clarified that if the core technical idea was known at the time of filing, whether the accused product produces the same effect as the patented invention should be determined by comparing individual functions and role of equivalents in the accused product to the corresponding claim element, rather than based on whether the core technical idea is embodied in the accused product.

It is the general principle in determining patent infringement to allow broader protection for an invention with high contribution to the development of technologies, while allowing narrower protection for an invention with low contribution. The Supreme Court’s decision above implies that infringement under the doctrine of equivalents may be narrowly or broadly determined depending on whether and how a core technical idea of the patented invention is novel in view of the specification of the patented invention and the prior art at the time of filing.