When drafting patent applications, the specter of a "design choice" rejection looms large for practitioners. According to the Manual of Patent Examining Procedure (MPEP) § 2144.04, a rejection based on design choice can arise when the examiner asserts that the claimed feature represents an arbitrary selection between alternatives that perform the same function in substantially the same way. While design choice can be a valid basis for rejection, there are steps one can take when drafting the specification to reduce the chances of falling into this trap.
Per MPEP § 2144.04, a design choice rejection hinges on the principle that “[a]n obviousness rejection based on a design choice is appropriate where the applicant has not shown that the particular design provides any unexpected results.” The examiner may argue that the claimed feature or configuration is an obvious variant of prior art because it does not yield a functional or technical benefit beyond what was already known. Note several previous posts on design choice (here, here, and here for example).
Notably, if an applicant cannot demonstrate a clear functional relationship or advantage associated with the claimed design, the examiner’s rejection is more likely to stand.
A recent decision by the Patent Trial and Appeal Board (PTAB) underscores the pitfalls of failing to preemptively address potential design choice arguments. Appeal 2023-003355, Application 16/430,848. Claim 1 is reproduced below:
1. A refrigerant compressor, comprising:
a first compression stage arranged in a main refrigerant flow path, wherein the first compression stage is a mixed compression stage having both axial and radial components;
a second compression stage arranged in the main refrigerant flow path downstream of the first compression stage,
wherein the second compression stage is a radial compression stage, wherein, upstream of the first compression stage, the refrigerant compressor is arranged such that fluid is configured to flow along the main refrigerant flow path in a first direction,
wherein, within the first compression stage, the refrigerant compressor is arranged such that fluid is configured to flow along the main refrigerant flow path in a second direction non-parallel to the first direction,
wherein, for substantially an entirety of a distance between the first compression stage and the second
compression stage, the refrigerant compressor is arranged such that fluid is configured to flow along the main refrigerant flow path in a third direction, and
wherein the third direction is substantially parallel to the first direction, substantially parallel to an axis of rotation of the refrigerant compressor, and spaced radially outward of the first direction.
The examiner rejected the claims on the basis that it was obvious design choice to modify the prior art’s refrigerant flow path to be substantially parallel to an axis of rotation of the refrigerant compressor for substantially an entirety of a distance between the first compression stage and the second compression stage. In essence, it seemed that the examiner considered differences in flow direction between the stages was mere design choice.
The applicant’s specification did not link the flow direction to any specific technical problem or advantage. When the applicant finally argued that the claimed combination provided unique benefits, this argument was presented in a reply brief—too late to be considered under 37 C.F.R. § 41.41(b)(2). And even when the PTAB tried to consider this late argument, the specification itself was cited by the PTAB to bolster, rather than undercut, the design choice rejection. The PTAB noted that the specification described two opposite flow configurations without any explanation of why one might be preferred or how either contributed to solving a problem. From the PTAB’s decision (citations omitted):
In its Appeal Brief, Appellant acknowledges the Examiner’s use of design choice, but does not dispute the Examiner’s findings on this issue in its Appeal Brief. That is, Appellant does not even allege that different flow directions between the stages solve any stated problems or are for any particular purpose. … In its Reply Brief, Appellant alleges for the first time that “the overall claimed combination is disclosed as providing a unique benefit, as discussed in the Brief at pages 1 and 2” and “Appellant’s claimed combination is disclosed as providing a benefit.” That argument is not entitled to consideration. … Nevertheless, even if considered, Appellant’s Reply Brief argument does nothing to identify Examiner error. The portion of the Appeal Brief referenced by Appellant says nothing about any purported “unique benefit” provided by the flow path between the first and second compressor stages being parallel to the axis of rotation of the compressor. And Appellant’s Specification, itself, appears to support the Examiner’s design choice rationale by providing two essentially opposite arrangements, as discussed above, with no discussion in the Specification as to why either one would be preferred.
To reduce the chances of succumbing to design choice rejections, consider the following strategies when drafting the specification. While there are always opposing issues to be balanced, there can be situations where such description might be worth including:
Identify Technical Functions: describe how specific features or groups of features contribute to the technical operation of the invention. Reduce generic language that implies equivalence between alternatives unless such equivalence is advantageous.
Highlight Advantages: Link each feature or configuration to tangible benefits, such as improved efficiency, durability, or reliability. For example, if a particular flow direction in a compressor reduces energy consumption, state this explicitly in the specification.
Address Alternatives: When alternatives are disclosed, explain why the claimed option is selected. For instance, if both clockwise and counterclockwise flow directions are described, indicate which direction is preferred and why and in which situation—even if the reason is application-specific.
Incorporate Experimental Data: If feasible, include test results or examples that demonstrate the advantages of the chosen design as compared to what otherwise be considered design equivalents. Empirical evidence can be a useful tool for overcoming allegations of obviousness or design choice.
The PTAB’s decision in the refrigerant compressor case illustrates the risks of omitting technical explanations in the specification. A lack of functional and advantageous detail not only invites design choice rejections but can also provide examiners with ammunition to sustain them.
By linking each claimed feature to a specific technical purpose and advantage, it is possible to strengthen the application’s ability to withstand scrutiny. At the same time, one should balance such description with disclosure that might be used to overly-limit claims during enforcement, for example.