Simply Rewriting Dependent Claims into Independent Form May Bar The Application of the Doctrine of Equivalents

By Dennis M. Smid and William S. Frommer

Patent applications submitted to the United States Patent and Trademark Office typically contain at least one independent claim and a number of dependent claims (each of which depends directly or indirectly from an independent claim). Many times, in an office action, the Examiner will reject an independent claim and will state that a dependent claim which depends from the rejected independent claim will be allowed if rewritten in independent form. In response to such office action, the applicant may merely cancel the rejected independent claim and rewrite the allowable dependent claim in independent form, resulting in the issuance of the patent. Now, due to a recent Federal Circuit decision1 , such response may give rise to prosecution history estoppel which, during a subsequent infringement suit, may bar the application of the doctrine of equivalents2 to the limitations contained in the dependent claim. In other words, merely rewriting the dependent claim in independent form and canceling the independent claim from which it originally depended may reduce the scope of this claim.

In Honeywell International Inc. v. Hamilton Sundstrand Corporation3 , Honeywell brought suit against Sundstrand in the U.S. District Court in Delaware for infringement of claims 8, 10, 11, 19, and 23 of U.S. Patent No. 4,380,893 and claim 4 of U.S. Patent No. 4,428,194.

Of the asserted claims only claims 8 and 9 of the '893 patent and claim 4 of the '194 patent are independent claims. Each of these independent claims was originally written as a dependent claim which included limitations of an inlet guide vane. The independent claims from which claims 8, 9, and 4 depended did not recite an inlet guide vane limitation. During prosecution of the '893 and '194 patents, each of these dependent claims was indicated to be allowable if rewritten in independent form, and the independent claims from which the dependent claims depended were rejected based on prior art. In response, the rejected independent claims were canceled and the allowable dependent claims were rewritten into independent form.

This case was tried before a jury which found Sundstrand had infringed claims 8, 10, 11, 19, and 23 of the '893 patent and claim 4 of the '194 patent under the doctrine of equivalents. Sundstrand appealed.

On appeal, the CAFC4 stated that this case requires first, to determine whether a narrowing amendment to a patent claim that adds an additional claim limitation creates a presumptive surrender of equivalents. The CAFC held that it does - and this of course is the classical example of prosecution history estoppel.

Next, the CAFC addressed the issue of whether rewriting an allowable dependent claim into independent form, coupled with the cancellation of the original independent claim, constitutes a narrowing amendment. In its analysis, the CAFC stated that there is no question that the original independent claims were rejected for reasons related to patentability (they were all rejected as being obvious in view of the prior art). These rejected independent claims were canceled and the dependent claims were rewritten into independent form to secure their allowance. The CAFC went on to state that a "presumption of surrender therefore arises if rewriting the dependent claims into independent form, along with canceling the original independent claims, constitutes a narrowing amendment."

Honeywell argued that "prosecution history estoppel cannot occur where a dependent claim is merely rewritten into independent form...[and contended] that, although it surrendered its broader independent claims, there is no presumption of surrender [of equivalence of the dependent claim] because the scope of the rewritten claims themselves has not been narrowed."

The CAFC disagreed with Honeywell and reiterated the rule it has consistently applied in post-Festo decisions: "the fact that the scope of the rewritten claim has remained unchanged will not preclude the application of prosecution history estoppel if, by canceling the original independent claim and rewriting the dependent claims into independent form, the scope of subject matter claimed in the independent claim has been narrowed to secure the patent." The CAFC held there is a presumptive surrender of all equivalents to the element (i.e. the inlet guide vane limitations) in the dependent claims. As such, Honeywell is presumptively estopped from recapturing equivalents to the inlet guide vane limitations originally contained in the dependent claims.

Consistent with the post-Festo CAFC decisions, Honeywell can rebut this presumption of surrender by showing either: (i) that the alleged equivalent would have been unforeseeable at the time of the narrowing amendment, (ii) that the rationale underlying the narrowing amendment bore no more that a tangential relation to the equivalent in question, or (iii) that there was some other reason suggesting that the patentee could not reasonably have been expected to have described the alleged equivalent.

* * *

The following suggestions may lessen or avoid the negative effects of the above-described Honeywell case:
  1. Write dependent claims in means plus function or step plus function form. Although means plus function dependent claims which are rewritten in independent form during prosecution may not be entitled to equivalents under the doctrine of equivalents (in accordance with the above Honeywell case), they may still be entitled to equivalents under 35 U.S.C. 112, sixth paragraph.

  2. Write a separate independent claim for each important feature of the invention. Although the CAFC in Honeywell did not specifically address the issue of when during prosecution of an application having a broad independent claim (e.g. containing elements A, B, and C) and a narrow independent claim (e.g. containing elements A, B, C, and D) the narrow independent claim is indicated to be allowable and the broad independent claim is rejected and subsequently canceled, is there a presumptive surrender of all equivalents to element D, the authors would not be surprised if the CAFC extended its ruling in Honeywell to cover this situation.5 To possibly avoid this, common elements in each independent claim should be worded somewhat differently from each other. For example, if independent claim 1 contains elements A, B, and C and it is desirable to claim what is in claim 1 plus element D, then independent claim 2 should be worded so as to contain elements A', B', C', and D.

  3. When a dependent claim is indicated to be allowable and the independent claim from which it depends is rejected and when it is desirable to obtain a patent quickly directed to the dependent claim, rewrite the dependent claim in independent form, cancel the independent claim and state that you will continue prosecution of the rejected claim in a continuation application, and file such continuation application and continue prosecuting the rejected independent claim. In Honeywell, the CAFC indicated that the "presumption of surrender" arises if the dependent claim is rewritten into independent form and the original independent claim is canceled. Here, it could be argued that since a continuation application was filed directed to the independent claim, the independent claim was not canceled.

  4. Ensure that applications are originally submitted with independent claims which reasonably distinguish over the known prior art. To assist in this, patentability searches should be conducted.

1Honeywell International Inc. v. Hamilton Sundstrand Corporation, 2004 WL 1202997 (Fed. Cir. 2004)

2"The doctrine of equivalents allows the patentee to claim those insubstantial alternations that were not captured in drafting the original patent claim but which could be created through trivial changes. ... An element in the accused device is equivalent to a claim limitation if the only differences between the two are insubstantial." Id. at *6.

3Honeywell Int'l, Inc. v. Hamilton Sundstrand Corp., 166 F. Supp. 2d 1008, 1015 (D. Del., 2001)

4U.S. Court of Appeals for the Federal Circuit.

5See FN 8 in Honeywell International Inc. at *16.

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