How does the Doctrine of Equivalents work in United States patent law?

A patent is a set of exclusive rights granted by a government to the inventor of an invention. To be granted a patent an inventor must demonstrate that the invention is worthy of a patent. An invention must be new, novel and not obvious to be granted patent protection. An inventor that is granted a patent gets the exclusive right to make use and sell the invention for a set period of time. If someone other than the patent owner makes, uses or sells during the term of the patent, that is considered patent infringement.

Sometimes competitors of a patent owner will attempt to make a product which is similar to the patented invention, but just different enough that the patent is not infringed. When a competitor wants to avoid patent infringement it is not enough to change a few features of the product. Courts in the United States have long recognized that a product or process which does not literally infringe a patent can still infringe a patent if it is equivalent to the claimed invention. This legal concept is known as the doctrine of equivalents.

The doctrine of equivalents is a concept a patent owner can use to file a patent infringement claim even though a product is not completely identical to the patented invention.

The United States Supreme Court has articulated two ways to apply the doctrine of equivalents.

The function-way-result test: “whether the accused product performs ‘substantially the same function in substantially the same way to obtain the same result’”

The insubstantial differences test: “whether the accused product or process is substantially different from what is patented.”

Examples of court decisions help illustrate how this concept works:

Warner-Jenkinson Company, Inc. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997) – The patent stated that a chemical process must have a pH level between 6.0 and 9.0 the infringing chemical process used a pH of 5.0. The United States Supreme Court remanded the case to the trial court to give the patent owner an opportunity to present evidence as to why the lower limit of 6.0 pH was included in the patent claims. This case is notable because the Supreme Court did not find for the defendant merely because the infringing product was different than the patented invention.

Deere & Co. v. Bush Hog, LLC, 703 F. 3d 1349 (Fed.Cir. 2012) – The patented invention, a grass cutter, had two elements which were directly connected. The infringing product had similar elements which were not directly connected. The District Court held that there was not patent infringement because the machines were different. The Federal Circuit reversed and held that there was patent infringement because in every case applying the doctrine of equivalents at least one claimed element is not literally present in the accused product.

Brilliant Instruments, Inc. v. Guidetech, LLC – (Fed.Cir. 2013) – A patented invention and an infringing product differed in the placement of a capacitor on a circuit board. Expert testimony at trial said that the capacitor performed the same function even though the circuit was different. The Federal Circuit held that function-way-result test was satisfied.

Intendis GmbH v. Glenmark Pharmaceuticals Inc., USA, 15-1902 (Fed. Cir. 2015) – The patented chemical claimed triglyceride and lecithin and the infringing chemical was formulated with isopropyl myristate. In both cases the chemicals performed the same function, even though the patent did not explicitly state what the function was. The Federal Circuit affirmed the District Court’s finding of infringement. The Federal Circuit held that evidence presented at trial can be used to determine the function of a component.

Mylan Institutional LLC v. Aurobindo Pharma Ltd., 17-1645 (Fed. Cir. 2017) – The patented chemical claimed silver oxide and the infringing product used magnesium oxide. The district court used the function-way-result test to determine that there was patent infringement, the Federal Circuit affirmed the District Court’s ruling but stated the insubstantial differences test is more appropriate in chemical patent cases.

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