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BRINGING LAW TO YOUR IDEAS
DOCTRINE OF EQUIVALENTS LIMITED FOR DEPENDENT CLAIMS
REWRITTEN IN INDEPENDENT FORM
By Jay Halt
The United States Court of Appeals for the Federal Circuit recently limited the
application of the Doctrine of Equivalents for claims that did not change in scope
during prosecution at the U.S. Patent and Trademark Office, but changed in form,
from dependent to independent. In Honeywell International Inc. v. Hamilton
Sundstrand Corporation, decided in June 2004, the Federal Circuit reversed a
finding of infringement by equivalents for an asserted claim that had been
rewritten in independent form during prosecution of the patent, even though the
scope of the rewritten claim had not changed.
In this case, Honeywell's invention established a "set point" representing the
minimum flow at which a surge in an Auxiliary Power Unit (APU) could safely be
avoided. Honeywell's patent claimed controlling the value of the set point using
adjustable inlet guide vanes. During prosecution of the Honeywell patent, several
originally pending dependent claims were only rejected as being dependent upon a
rejected base claim. The dependent claims, to which no substantive amendments
were made, were subsequently rewritten into independent form and allowed. To
most practitioners, this would indicate that one or more of the features recited in
the dependent claims were novel and unobvious, including the claimed controlling
of the set point value using adjustable inlet guide vanes.
The accused infringer, Sundstrand, manufactured an APU which also uses an
active surge control system that compares a flow-related parameter to a set point
and adjusts the surge bleed valves in response. Sundstrand's device establishes a
set point that is dependent upon ambient air temperatures rather than a
measurement of inlet guide vane position. The Sundstrand APU blocks control
signals used to operate the surge bleed valve during extreme high flow conditions.
The determination of whether to block these control signals is based, in part, upon the
position of the inlet guide vanes.
Honeywell had conceded at the trial court that the inlet guide vane limitation in its
claim was not literally met by the accused Sundstrand device. However, Honeywell
successfully argued at the trial court that the position of the bleed control valve in
Sunstrand's system was controlled, at least in part, by the position of the inlet
guide vanes which resulted in a finding of infringement under the Doctrine of
Equivalents.
On appeal, the Federal Circuit held that rewriting a dependent claim into
independent form is a narrowing amendment, which bars the application of the
Doctrine of Equivalents for the subject matter added from the dependent
claim to the original subject matter of the independent claim. This appears to
be counter-intuitive because the subject matter for which equivalents are
barred is in fact the very subject matter from the dependent claim that the
patent examiner found to be novel and unobvious over the prior art.
As a result, the generally accepted practice of filing one or more independent
claims and a series of dependent which further narrow the independent claim can
result in an unintentional loss of equivalents during prosecution, even if the scope
of a dependent claim never changes. Several strategies have been discussed for
dealing with this potential loss of equivalents for the very features of an invention
which are novel and unobvious over the prior art. One suggestion, alluded to in a
dissenting opinion of one Judge, is filing all claims in independent form. This
would involve additional filing costs, and could potentially be more
cumbersome for an examiner reviewing the application. However, it would
currently avoid the Honeywell bar to equivalents. Alternatively, writing the
patent specification to recite all known structural equivalents for any features
believed to be novel and including “means plus function” limitations in the
claims would at least allow for structurally equivalent elements to be covered
by such claim limitations if they perform the identical function, which would
not appear to have been the case in Honeywell
This field of law is constantly developing and changing, and it would not be surprising
to see the lost Honeywell equivalents resurrected in the future.