US 3994020

I'll search for authoritative information on this patent number.

Let me double-check the CAFC/docket angle with more specific queries.

US 3,994,020 — Verification & Summary

Search note up front: I searched for the specific number 3994020 in the USPTO/patent-document space and for any 2026 CAFC docket activity. I found no Court of Appeals for the Federal Circuit docket, appeal, or 2026 litigation involving US 3,994,020. That is consistent with the fact that this patent is long expired (Google Patents records an "Anticipated expiration" of 1993‑11‑30 and a legal status of "Expired – Lifetime"). I also confirmed no claim of current 2026 CAFC activity for this number exists in the search results returned. Treat "no CAFC docket found" as a negative search result, not affirmative proof of non-existence.

Identifier-collision warning (do not auto-correct): one search hit for "EP 3994020" is an unrelated European patent document — "A fuel gas system for a vehicle" (EP 19739942 A / WO2021001027A1). That is a different numbering system and a different invention. Do not conflate the two. Similarly, US 3,994,020 is distinct from its same-day sibling cases US 3,994,021 and US 3,994,022.

Bibliographic data

Prosecution / ownership history (as listed): assigned from The Kendall Company to Athletic Helmet, Inc. (1986‑11‑06); security interests recorded to Bank of New England, N.A. (1986‑11‑06) and First American National Bank of Nashville (1988‑02‑11); release by secured party 1992‑01‑10.

Foreign family (same 1975‑06‑05 priority): AU500960B2, GB1513841A, CA1059251A, FR2312982A1, IT1062011B, BE842652A, DE2625211A1, SE410377B, NZ181064A, MX4168E, NL7606095A, ZA763349B, JPS52547A, plus later CA1059261A.

Source: https://patents.google.com/patent/US3994020/en (full text supplied) and https://patents.justia.com/patent/3994020

Abstract (verbatim)

"A protective helmet comprising a shell, and liner means positioned on the inside of the shell for absorbing impacts applied against the helmet. The liner means has a plurality of fluid-filled chamber means generally aligned intermediate the wearer's head and the shell, with at least two of the aligned chamber means being deformable in differing amounts responsive to a given force level applied against the helmet."

Plain-language overview of each independent claim

Claim 1 — Differential-hardness, aligned fluid chambers (broadest concept).
A helmet with a shell and a liner inside it. The liner's walls are flexible and define several fluid-filled chambers sitting one behind another (aligned) between the head and the shell. Key point: the wall material forming at least two of those aligned chambers has different hardnesses, so those two chambers compress by different amounts under the same impact force. (Note: "different hardnesses" — physical material property — rather than durometer of a whole liner.)

Claim 2 — Soft-inner/hard-outer arrangement, claimed functionally.
Same shell-plus-fluid-chamber structure, but the two aligned chambers are specifically designated "first" (toward the head) and "second" (between the first chamber and the shell). The first chamber is more easily compressed at relatively low force levels than the second chamber. This is the low-force-vs-high-force split of energy absorption.

Claim 3 — Single liner means with two distinct portions.
A shell plus flexible liner means having (a) a relatively soft inner portion with a first fluid-filled chamber that presents a soft head-contacting surface, and (b) a harder second portion (harder than the first) with a second fluid-filled chamber located between the first chamber and the shell. The harder portion deforms less at a given force so it handles higher-level forces.

Claim 4 — Two separate liners that cooperate (the commercial heart of the disclosure).
A shell; a first inner liner of flexible material with first fluid-filled chamber means and a soft conformable head-contacting surface; and a second flexible liner between the first liner and the shell, with second fluid-filled chamber means at least partly between the first chamber and the shell. The second liner is less deformable than the first at a given force level. The two liners "co‑operate to dissipate varying levels of forces... while providing comfort to the wearer." Dependent claims 5–20 build on this: Shore A 45–55 for the first liner (claim 5); Shore A 75–90 for the second (claim 6); gas fill (7, 8); inflation valve through the shell for the second chamber (9) and inside the helmet for the first (10); roto-molding (11); PVC plastisol/EVA/polyethylene/liquid polyurethane (12); aligned hollow radial spokes (13), hollow rim (14), hollow annular member (15); first liner removably nested in the second (16); same shape (17); elastic material (18); first liner's modulus of elasticity less than the second's (19); liquid fill in the second chamber (20).

Claim 21 — The liner assembly claimed per se (no shell).
Liner means for headgear: a first liner with flexible walls defining a first fluid-filled chamber, and a second liner with flexible walls defining a second fluid-filled chamber. The second liner's walls have a lower durometer hardness than the first liner's walls, and the second liner sits inside the first liner with at least part of its chamber generally aligned with the first chamber. (Caution: the claim's "first/second" and "inside" language is inverted relative to the intuition that the soft liner touches the head — read it literally.) Claims 22–23 add that the low-durometer second-liner wall provides the soft head-contacting surface, and the high-durometer first-liner wall provides the rigid high-force structure.

Claim 24 — The spoke/wheel liner geometry claimed per se.
Liner means for headgear comprising a flexible liner having a hollow annular member defining an opening that passes through the liner near its upper central part, plus a plurality of hollow spoke members that communicate with and extend radially from that annular member. Dependent claims 25–27 add an inner second liner with its own annular member and radial hollow spokes, alignment between the two, and gas inflation with the outer liner more rigid than the inner (as drafted: "the inflated first liner is more rigid than the inflated second liner").

Claim 28 — Modulus-of-elasticity variant of the two-liner helmet.
A shell; a first inner liner of elastic material with first fluid-filled chamber means and a head-contacting inner surface; and a second liner of elastic material between the first liner and the shell with second fluid-filled chamber means. The first liner has a lower modulus of elasticity than the second, so the inner surface conforms to the head while the second liner is rigid enough to dissipate high-level forces.

Context and caveats

• The specification's disclosed embodiment is a football helmet (expressly extendable to hockey, baseball, crash helmets) with two rotomolded, nestable, inflatable "spoke-and-rim" liners: soft inner liner 52a (Shore A 45–55) and harder outer liner 52b (Shore A 75–90), plus foam retainer pads 70 in the triangular liner openings, a top pad 114, front/rear sizing pads 90/84, a PORON sweat band 96, jaw pads 120, and a chin strap 146. Alternative embodiments (FIGS. 23–27) replace or supplement the second inflatable liner with a molded foam third liner 174, a closed-cell vinyl foam second liner 180, or a peripheral third resilient liner 192.
• Relevant to your CAFC question: US 3,994,020 is cited as prior art in modern helmet-patent proceedings (I saw it in IPR petition papers for helmet patents referencing "Weber," at ptacts.uspto.gov). It is a cited reference there, not the patent on appeal. No 2026 Federal Circuit docket naming US 3,994,020 appeared in my searches.
• Uncertainty disclosure: the assignee/reassignment entries and the 1993 expiry date come from Google Patents' derived data (which itself disclaims legal-status accuracy), not from a direct live USPTO Patent Center or assignment-database query — I could not independently confirm them from a primary USPTO record in this session. Where "current assignee" is stated, treat it as the listed data, not a legal conclusion.

I'll research litigation involving US patent 3994020.

Let me search litigation-specific databases.

Let me run more targeted searches on litigation databases.

Litigation Search Results — U.S. Patent No. 3,994,020

Bottom line

I found no evidence of any litigation in which U.S. Patent No. 3,994,020 was asserted, challenged, or otherwise at issue as a patent-in-suit. I also found no PTAB, ITC, or foreign counterpart proceedings directed at this patent. Below I explain what I checked, what I found, and important caveats.

Patent identification (to confirm I searched the right patent)

Per the authoritative full text you provided (Google Patents, https://patents.google.com/patent/[US3994020](/patent/US3994020)/en):

Two points from this record have direct bearing on the litigation question:

1. The patent lapsed in 1993. Any U.S. infringement action would necessarily have been filed during its enforceable life (1976–1993). Post‑issuance AIA proceedings (IPR/PGR/CBM) did not exist before 2012 and could not have targeted an already‑lapsed patent, so the absence of PTAB cases is expected rather than surprising.
2. The recorded security interests (Bank of New England, N.A. and First American National Bank of Nashville, both later released by their secured parties) are financing/assignment events of Athletic Helmet, Inc., not litigation.

What the searches returned

• Searching for litigation on 3994020 surfaced only prior-art citations, not lawsuits:
  • U.S. Patent No. 3,994,020 is listed as a U.S. Patent Document reference on later helmet patents (e.g., Justia pages for D965908 "Soft gear helmet" and D729983 "Helmet padding system"; FreePatentsOnline page for Riddell's US 7,954,177 "Sports helmet").
  • The Riddell US 7,954,177 reference list also contains litigation documents from Riddell, Inc. v. Schutt Sports, Inc., No. 08‑cv‑711 (W.D. Wis.). Important: that case concerned Riddell's US 7,954,177, not US 3,994,020. In that record 3,994,020 appears at most as a cited reference in the prior-art/prosecution history — it was not the patent being asserted. I would not report this as "litigation involving 3,994,020."
• Searches of the Unified Patents litigation portal, PTAB petition documents, and general CAFC/PACER‑oriented queries returned no hit tying case dockets to US 3,994,020. (Note: my searches surfaced documents about Unified Patents generally — RPI disputes, amicus briefs — none of which reference this patent.)

Caveats — please read

• My tool access was exhausted before I could complete every planned database query (including direct Docket Navigator / PACER / CourtListener lookups and a full run of the Unified Patents case list at https://portal.unifiedpatents.com/litigation/caselist). I cannot represent this as an exhaustive, exhaustive‑across‑all-districts search.
• Do not auto‑correct the number. I did not substitute a similar identifier. One unrelated result concerned EP 3 994 020 (a European patent for "A fuel gas system for a vehicle," Hitachi/Air Products‑type subject matter) — that is a different patent in a different jurisdiction and is not relevant to US 3,994,020.
• Pre‑1993 district court dockets from the paper era are often not fully indexed in electronic commercial databases, so a genuinely exhaustive answer for a 1976–1993 patent would require a manual review of the Federal Reporter/U.S.P.Q. volumes and the patent's own file wrapper (assignment/license records). The absence of hits is evidence, but not proof, of no litigation.
• Nothing in the assignment history for this patent (1986 security interests and releases) shows an exclusive license or transfer that would obviously have triggered an enforcement campaign, but I did not verify license agreements.

Conclusion

No litigation involving U.S. Patent No. 3,994,020 is known or documented in the sources I was able to reach. The only appearances of this number are as prior art cited against, or listed on, later patents, and the only litigation-adjacent context is Riddell, Inc. v. Schutt Sports, Inc., No. 08‑cv‑711 (W.D. Wis.), which is about a different, much later Riddell patent. If you need certainty, the next step would be a paid Docket Navigator / Lexis Patent Litigation search plus a manual check of the 1976–1993 United States Patents Quarterly for "3,994,020" or "Villari"/"Athletic Helmet, Inc." — I can outline that search protocol if useful.

I'll verify the structured block's "no PTAB activity" default against public sources before writing.

The first pass surfaced only look-alike numbers ('399 patent family, EP 3994020 for a fuel-gas system) — none involving US 3,994,020. Let me run a few more targeted checks.

One more diligence pass on reexaminations and any descendant/related-patent PTAB activity that could be confused with this patent.

Proceedings overview

Total AIA trial proceedings on file: 0. The USPTO Open Data Portal returns no IPR, PGR, or CBM proceeding naming US 3,994,020, and my independent web checks (Google Patents litigation/PTAB tab, PTAB E2E/PTAB API queries, and general searches on the patent number, inventor name, and assignee) surfaced no petition, institution decision, Final Written Decision, or Federal Circuit appeal — only look-alike distractors (the unrelated '399 patent family, the fuel-gas EP 3994020, and sibling Villari helmets US 3,994,021 / 3,994,022). The breakdown is therefore: active 0 / claims invalidated 0 / claims sustained 0 / settled 0 / institution denied 0. Defensive posture: not "hardened by IPRs" and not "narrowed by IPRs" — the correct read is that no AIA-challenge record exists at all, and none can meaningfully exist, because the patent expired on 1993-11-30 and AIA trials did not begin until 2012-09-16.

No proceedings to list

Because the count is zero, there is no most-impactful-first ordering to produce. To be explicit about what I did and did not find:

• No IPR. No IPR petition against US 3,994,020 appears in the USPTO ODP/PTAB structured data or in public indexes.
• No PGR — and none is statutorily possible. Post-grant review under 35 U.S.C. § 321(c)/§ 321(d) is available only for patents issued under the first-inventor-to-file regime (effective 2013-03-16). US 3,994,020 has a 1975-06-05 filing date and 1976-11-30 grant date, so it is a pre-AIA patent and PGR was never available against it.
• No CBM — and none is statutorily possible. Covered business method review was limited to patents claiming a "financial product or service." A protective football helmet with inflatable liners is not a covered business method patent.
• No Federal Circuit appeal. With no FWD, there is nothing to appeal. My searches returned no CAFC docket or CourtListener entry arising from a PTAB decision on this patent.
• Non-AIA PTAB/Office history (unverified). PTAB also handled interferences and ex parte reexaminations before 2012, and those do not appear in the ODP "AIA trial proceedings" feed. I found no public evidence of an interference or reexamination involving US 3,994,020, but I could not complete that verification before running out of search budget — flagging it as unconfirmed, not as a finding either way. Nothing I saw suggests one exists.

Strategic summary

Claim status: all 28 claims are UNTESTED (never challenged at the PTAB), but that is academic — the patent is expired. Claims 1–4 (the independent helmet claims), claims 21 and 24 (independent liner-means claims), and claim 28 (independent helmet claim) were never canceled, never amended, and never construed by the Board. They were also never affirmed. Claim 1 requires a shell plus liner means with flexible wall means defining fluid-filled chambers where "separate portions of the wall means defining at least two of said aligned chamber means have different hardnesses"; claims 5 and 6 recite the 45–55 and 75–90 Shore A ranges, and claims 7–8 and 20 recite gas and liquid fills. Under 35 U.S.C. § 318(b), no IPR certificate ever issued, so the claim set stands exactly as it printed in 1976 — it simply ceased being enforceable when the term ran out. Per the Google Patents record, the patent's legal status is "Expired – Lifetime," with an anticipated expiration of 1993-11-30.

Estoppel landscape: none, because there is no proceeding. Section 315(e)(2) estoppel attaches only to a petitioner whose IPR reached a final written decision. With zero IPRs, there is no petitioner-side estoppel on this patent, and no IPR-related bar limits anyone's prior-art arguments. The practical restraint on a defendant is entirely different: an expired patent cannot be infringed, so damages are limited to the six-year lookback in 35 U.S.C. § 286 running backward from the filing of a complaint — and that window closed in 1999. Any demand letter invoking US 3,994,020 today is asserting a dead patent. The availability of IPR "any time after grant" for pre-AIA patents (per USPTO's own AIA-trial chart) is theoretical here: an expired patent supports no infringement claim and thus no realistic petitioner standing or fee spend — which is precisely why 34 years of post-expiration history generated not one petition.

Pattern signals: no repeat petitioner, no patent-owner appeal history, and no defensive aggregator (Unified Patents or similar) involvement is visible for this patent. The relevant pattern is genealogical, not adversarial: the family is the Villari/Kendall Company line of 1976 helmet patents (US 3,994,020, 3,994,021, 3,994,022), with a Kendall continuation-style sibling US 4,062,068 (chin strap, priority 1976-10-20). Later patents in the space — e.g., Riddell's inflatable liner US 5,175,889 and Maxpro's gas-fitted helmet US 5,014,365 — are in the Cited By branch, i.e., they cite 3,994,020 as background art rather than attacking it. If a defendant is actually facing a helmet-patent demand, the live risk almost certainly sits on one of those later, still-in-force patents (Riddell, Kranos, Bell, Matscitechno, etc.), not on the 1976 Villari patent.

Recommended next steps

• If a demand letter cites US 3,994,020: the answer is statutory, not evidentiary. The patent expired on 1993-11-30 (Google Patents legal status: "Expired – Lifetime"). Confirm the expiration and the absence of any post-expiration reissue or reexamination through the USPTO PatentCenter record (https://patents.google.com/patent/US3994020/en) and the official file wrapper (https://patentcenter.uspto.gov). A demand premised on an expired patent — with the § 286 recovery window having closed in 1999 — should be rejected out of hand.
• If the demand letter cites a different helmet patent that cites 3,994,020 as art: redirect the analysis. 3,994,020 is a prior-art reference to those patents, which makes it a defensive asset — its 1975-06-05 priority date is available as § 102 prior art against later-issued helmet claims. Verify its status as a printed publication and its § 102(a)(1)/(a)(2) date before relying on it.
• If you want to confirm the zero-count independently: the PTAB E2E docket search and the USPTO PTAB API (https://developer.uspto.gov/api-catalog/ptab-api) are the canonical sources; CourtListener (https://www.courtlistener.com) and the Federal Circuit docket will confirm there is no FWD appeal. My searches of these returned no hits for proceeding numbers involving US 3,994,020, and I did not encounter any proceeding number I could cite — so I am not inventing one.
• Caveat on the absence as a signal: for a live patent, "no IPRs" is weak evidence of strength, since well-asserted patents attract challenges. Here the absence is not a strength signal at all — it is a function of the patent having expired roughly 19 years before AIA trials existed. Do not read the clean record as the patent having "survived" anything.

Sources consulted: US 3,994,020 full text and bibliographic/legal-status data (https://patents.google.com/patent/US3994020/en); USPTO ODP structured "PTAB proceedings on file" block (canonical, reports none); USPTO AIA-trial availability table (via uspto.gov PTAB inventor-hour materials) confirming IPR is the only AIA vehicle available against pre-AIA patents and that PGR is limited to first-inventor-to-file patents; Google Patents "Cited By" data for US 3,994,020.

I'll reconstruct the assignment record, starting with searches for the recorded USPTO assignments and reel/frame data.

Web search is returning prior-art citations rather than assignment-center records. Let me try a few more targeted queries for reel/frame data and the patent family's ownership history.

Assignment & Ownership Analysis — U.S. Patent No. 3,994,020

Source note / limitation up front. The authoritative Google Patents record you supplied exposes this patent's legal events (the "reassignment" block) but does not expose reel/frame numbers, correspondent attorneys, or execution dates — only recording dates and conveyance types. I attempted to reach the USPTO Assignment Center and third‑party mirrors via web search; the searches returned only prior‑art citations of 3,994,020 (Justia, FPO, Google Patents citation lists) and the unrelated EP 3 994 020 fuel‑gas patent. I could not retrieve reel/frame or correspondent data in this session. I will not invent reel/frame numbers. Where I rely on general knowledge rather than a retrieved source, I say so.

Inventors

Pattern check (inventor departure / fire‑sale precursor): not present, but not verifiable. There is no inventor‑to‑Kendall assignment recorded in the Google Patents legal‑events list (common — the original employment assignment frequently predates or is not surfaced as a "reassignment" event), and I found no evidence of Villari leaving Kendall. Notably, Kendall's helmet program continued after this filing: US 4,062,068 "Chin strap for protective headgear," priority 1976‑10‑20, granted 1977‑12‑13, assignee The Kendall Company, appears in this patent's own Cited‑By list. That continuity argues against the "all inventors departed within 12 months" fire‑sale tell. I could not confirm Villari's employment dates at Kendall.

Original assignee

The Kendall Company, a Delaware corporation ("KENDALL COMPANY, THE, A CORP. OF DE" per the recorded 1986 assignment entry; the issued face lists "The Kendall Company").

• Primary line of business: diversified healthcare/medical‑supply and textile manufacturing (the patent's own textile‑adjacent materials list — polyvinyl chloride plastisol, vinyl‑coated poromeric sheets — is consistent with a textiles/coatings manufacturer rather than a dedicated sporting‑goods firm). I was unable to re‑verify Kendall's corporate history in this session; the following is from general knowledge, lower confidence: Kendall was acquired by Colgate‑Palmolive in 1988, with the healthcare business later moving to Tyco Healthcare / Kendall Healthcare (1994) → Covidien → Medtronic.
• Did it ship a product embodying the claims? Unclear. Kendall filed and prosecuted a three‑patent helmet family in 1975 and added a chin‑strap patent in 1976, which indicates a real development program; but I found no evidence of a Kendall‑branded production football helmet. This matters, because it makes the 1986 divestiture look less like a "core business" sale and more like a divestiture of a non‑core technology line.
• Current status: Kendall as a distinct helmet‑owning entity no longer holds this patent. The patent was divested in 1986 and its U.S. legal status is "Expired – Lifetime," with "Anticipated expiration" recorded 1993‑11‑30 (failure to pay maintenance fees).

Assignment timeline

Records below are the recorded legal events from the authoritative source. Reel/frame is not exposed in that source and I could not retrieve it; correspondent of record is likewise unavailable. I therefore report conveyance, parties, and recording date, and explicitly mark the two data fields the task asks for that I could not obtain.

• 1986‑11‑06 (recorded; execution date not exposed) — Reel not available to me / Frame not available to me

  • Conveyance: Assignment of Assignors' Interest
  • Assignor: The Kendall Company, a corporation of Delaware
  • Assignee: Athletic Helmet, Inc.
  • Correspondent: not retrieved — flag: no correspondent data obtainable; no recurrence analysis possible
  • Context: Divestiture / acquisition — Kendall sold the helmet technology to a dedicated helmet maker, which simultaneously financed the purchase (see the same‑date lien below). The same‑day pairing of a sale and a security interest is the classic acquisition‑financing structure, not an NPE transfer.

• 1986‑11‑06 (recorded) — Reel not available / Frame not available

  • Conveyance: Security Interest ("see document for details")
  • Assignor: Athletic Helmet, Inc.
  • Assignee: Bank of New England, N.A.
  • Correspondent: not retrieved
  • Context: Securitization — the acquired helmet assets (this patent included) were pledged as collateral for acquisition/operating debt. A bank taking collateral on the operating company's own patents is an ordinary commercial‑lending event.

• 1986‑11‑06 (recorded) — Reel not available / Frame not available

  • Conveyance: License ("see document for details")
  • Assignor: Bank of New England, N.A.
  • Assignee: Athletic Helmet, Inc.
  • Correspondent: not retrieved
  • Context: Lienholder consent / license‑back — recorded the same day as the security interest, evidently documenting the lender's consent to the borrower's continued use and exploitation of the pledged assets. ⚠️ Anomaly flag: the recorded entries include what appear to be transposed or duplicate party fields (a "License" flowing from the bank to the borrower is unusual as a standalone conveyance, and the 1988 entry misspells the assignor as "ATHLETIC HELMUT, INC."). These look like clerical artifacts in the underlying index rather than separate economic events; I flag rather than resolve them.

• 1988‑02‑11 (recorded) — Reel not available / Frame not available

  • Conveyance: Security Interest
  • Assignor: Athletic Helmet, Inc. (recorded as "ATHLETIC HELMUT, INC." — literal transcription in source)
  • Assignee: First American National Bank of Nashville
  • Correspondent: not retrieved
  • Context: Refinancing — a second lender replaces/adds collateral coverage, again over the operating company's own patents. Two lenders over a six‑year window is a financing story, not an aggregation story.

• 1992‑01‑10 (recorded) — Reel not available / Frame not available

  • Conveyance: Release by Secured Party
  • Assignor: First American National Bank (formerly First American National Bank of Nashville)
  • Assignee: Athletic Helmet, Inc.
  • Correspondent: not retrieved
  • Context: Lien release / debt payoff — the last recorded event returns clean title to Athletic Helmet, Inc. No further assignment appears in the record, so Athletic Helmet, Inc. is the last recorded owner. The next recorded event is 1993‑11‑30 "Anticipated expiration."

Chain summary: The Kendall Company → Athletic Helmet, Inc. (1986), encumbered twice by commercial lenders, then cleared. No post‑1992 owner change is recorded.

Timeline diagram

timeline
    title Ownership of US 3994020
    1975 : Filed by The Kendall Company
    1976 : Patent issued
    1986 : Kendall assigns to Athletic Helmet Inc
         : Bank of New England security interest
    1988 : Security interest to First American Bank
    1992 : First American Bank releases lien
    1993 : Patent lapses for non payment

NPE / troll-pattern signals

Critical cross‑check: the prior section of this analysis found no litigation, PTAB, ITC, or foreign proceeding ever involving US 3,994,020. That is the baseline against which every signal below is measured — several of these tells are definitionally absent when a patent was never asserted.

Verdict

Defensive / non‑asserting — adapted

(Adaptation disclosed: the rubric's parenthetical for this verdict contemplates a chain terminating at a defensive aggregator. That is not what happened here. The chain terminates at an operating manufacturer — Athletic Helmet, Inc. — and then at statutory expiration. I select this category because the substantive conclusion it encodes, "the patent was neutralized and never used to extract value through assertion," is the one the evidence supports; no NPE category fits.)

Justification (2–3 sentences). Every recorded ownership event is an ordinary commercial transaction by operating companies: Kendall's 1986‑11‑06 divestiture of the helmet line to Athletic Helmet, Inc., twinned on the same day with a Bank of New England, N.A. security interest, followed by a 1988‑02‑11 refinancing lien to First American National Bank of Nashville and a 1992‑01‑10 release of that lien back to Athletic Helmet, Inc. Athletic Helmet, Inc.'s operating character is corroborated by its ownership of USD335366S (helmet design, 1993) and US 5,298,208 (helmet molding method, 1994), and the patent lapsed on 1993‑11‑30 with no assignment ever recorded to a shell LLC, aggregator, or known asserter, and no litigation ever filed. Insufficient data caveat: because I could not obtain reel/frame numbers or correspondent‑of‑record data, signals 3 and 6 remain unverified, and a single‑appearance correspondent check could not be run.

Verify at: USPTO Assignment Center — https://assignmentcenter.uspto.gov/ (search patent number 3994020) and the legacy mirror https://assignment.uspto.gov/patent/index.html. Retrieve reel/frame and correspondent for each of the five 1986–1992 events above to close the two open fields.

Suggested next steps to close the gaps

1. Pull the five reel/frame records from Assignment Center and record the correspondent of record verbatim (this is the single highest‑value missing data point for signal 3).
2. Check the Athletic Helmet, Inc. correspondence address across its four or more recorded patents (this patent, USD335366S, US 5,298,208, US 4,062,068‑family) for a single recurring attorney — that recurrence test is only runnable with the reel data.
3. Confirm whether Bank of New England's 1991 failure produced any assignment of this collateral to the FDIC — no such entry appears in the source record, but a manual file‑wrapper check would settle signal 6.
4. Verify Kendall's Colgate‑Palmolive (1988) / Tyco (1994) lineage via SEC filings if the corporate‑successor question matters — I flagged this above as unverified general knowledge.

I'll search for the specific prior-art citations listed on US 3,994,020, starting with the patent's own citation record.

Google Patents' scraped text omitted the "Patent Citations" (references-cited) table. Let me pull it from other mirrors.

I found the key "Referenced Cited" data on Justia. Let me get the complete citation list (front page) from additional mirrors.

Prior-Art Analysis — US 3,994,020 ("Protective helmet with liner means")

1. Per-reference summary table

Important caveat before the table. The authoritative Google Patents full text you supplied for US 3,994,020 does not contain the front-page "(56) References Cited" table — the scrape jumps from "Country Status (14)" straight to "Cited By (83)" and "Families Citing this family (6)." "Cited By" is forward citation data (later patents citing '020), which is not §102 prior art against '020. To answer your question I had to recover the backward citation list from a secondary mirror (Justia), and that retrieval returned only three U.S. patent documents. I could not reach the printed front page/PDF of the patent itself before my search budget was exhausted, so treat the list below as retrieved-data, not a verified complete list (see §4).

Sources: Justia "Referenced Cited" table for US 3,994,020 — https://patents.justia.com/patent/[3994020](/patent/3994020) ; SciSpace record "Protective helmet with liner means (1975) | Frank K. Villari | 48 Citations" — https://scispace.com/papers/protective-helmet-with-liner-means-15qd7g0go8

2. On your "USPTO database" instruction

I did not obtain these from a direct USPTO Patent Center / Patent Public Search query — I reached them via Google Patents (your authoritative text), Justia, FreePatentsOnline, and SciSpace. I want to be explicit about that rather than imply a USPTO-record provenance I did not achieve. The examiner of record (per Justia) was Primary Examiner G. V. Larkin, and the attorney of record appears as "Powell L." in the retrieved data (truncated; not worth relying on).

3. Reference-by-reference §102 analysis (provisional)

Recall the novelty pivot of the patent, from the claims you already have summarized: every independent claim (1, 2, 3, 4, 21, 24, 28) hinges on fluid-filled chamber means, with either two wall portions of different hardness (claims 1–3), two liners of different deformability/modulus (claims 4, 28), or a durometer differential between walls (claim 21). Only claim 24 (hollow annular member + radially extending hollow spokes, liner per se) is a pure geometry claim not expressly requiring a hardness differential.

US 3,462,763 (Schneider et al., Aug. 1969) — §102(b).
A pre-1975 U.S. patent in the protective-headgear/liner space, cited by the applicant/examiner as background. For this to anticipate any of claims 1–4 or 21–28 it must disclose two fluid-filled chambers arranged one behind the other between head and shell, with the two chamber-defining wall portions of different hardness (or two liners of different deformability). A conventional single foam or single air-cushion liner — the norm in 1969 art — would not meet that limitation and would be at most §103 background. I could not retrieve the reference text, so I cannot assert it does or does not disclose the differential-hardness feature. Provisional conclusion: no anticipation on the face of the retrieved data.

US 3,600,714 (Cade et al., Aug. 1971) — §102(b).
Same analysis, same result on the retrieved data. It is a §102(b) reference by date, but date alone does not create anticipation; the reference must disclose each claimed element. The critical missing element is again the plurality of aligned fluid-filled chambers of differing hardness/deformability. Provisional conclusion: no anticipation on the face of the retrieved data.

US 3,906,546 (Gooding, Sept. 1975) — timing is the dispositive point.
This patent issued roughly 2½ months after the June 5, 1975 filing date of US 3,994,020. That has two consequences:

• It cannot be §102(a) or §102(b) art (its publication/grant does not predate the filing, and it is nowhere near the one-year bar).
• It can only be prior art under pre-AIA 35 U.S.C. §102(e) — i.e., a U.S. patent granted on an application filed before the applicant's date of invention. Whether that applies turns on Gooding's U.S. filing date (typically 1973–74 for Gooding's helmet work) versus Villari's date of invention, neither of which was in my retrieved data.
• Practically, a reference whose grant postdates your filing is usually cited by the examiner as arguably-§102(e) art, and it carries Swearing-Behind risk rather than being an absolute bar. Provisional conclusion: not an anticipatory reference under §102(a)/(b); §102(e) applicability unverified.

Gooding, "Hand gun bullet proof protective headgear," 16 Apr. 1973 (number unconfirmed).
Reported as a back-citation only by SciSpace. If it is a U.S. patent with a 1973 issuance, it would be §102(b) art by date. There is a plausible overlap with claim 24 (and its dependents 25–27), because claim 24 claims the liner geometry per se — a flexible liner with a hollow annular member defining a through-opening and hollow radial spokes — without requiring a hardness differential. Any 1973 headgear patent teaching a multi-cell/spoke-type liner would deserve a hard look at claim 24 first. I did not confirm the patent number or its disclosure, so I am flagging this as a lead, not a finding.

Why claim 24 is the claim to focus your prior-art search on: claims 1–4, 21, 22–23 and 28 all require a fluid-filled chamber pair with a hardness/deformability differential, which is a narrow, specific structure. Claim 24 requires only a hollow annulus + hollow radial spokes. If a single reference anywhere discloses that geometry in a helmet liner, claim 24 (and its scope-limiters 25–27) fails before any hardness argument arises.

4. Verification gaps I am explicitly flagging (do not treat the above as complete)

1. The "(56) References Cited" table was not in the source text you supplied, and my Justia retrieval returned only three U.S. patent documents. Three U.S. citations is unusually sparse for a 1976 mechanical helmet patent, so the list may be truncated in the retrieved snippet. The authoritative front page of the printed patent (U.S. Patent 3,994,020, col. 1, "(56) References Cited") or the file wrapper in USPTO Patent Center must be checked to confirm whether additional U.S. or foreign documents, or "Other References," were listed.
2. I did not retrieve the full text, title, or abstract of any of US 3,462,763, US 3,600,714, or US 3,906,546. Everything above about what they disclose is therefore reasoned from the claim language outward, not read off the references. Do not represent these as substantive §102 findings until the reference texts are read.
3. US 3,906,546's filing date and US 3,994,020's date of invention are both unknown to me, so the §102(e) question is open, not resolved.
4. The 1973 Gooding reference's patent number was not confirmed. I deliberately did not assign a number.

Recommended verification steps: (a) pull the printed front page of US 3,994,020 to capture the complete (56) list; (b) pull full text of 3,462,763 / 3,600,714 / 3,906,546 from USPTO Patent Public Search or Google Patents and check specifically for two fluid chambers and for any hardness/durometer/differential-deformability teaching; (c) confirm 3,906,546's filing date; (d) confirm the Gooding 1973 document's number.

5. Identifier hygiene (carried forward, because it matters here)

• US 3,994,020 (Kendall, Villari) is not its same-day siblings US 3,994,021 and US 3,994,022 (Villari et al.), nor the 1977 Kendall US 4,062,068 ("Chin strap for protective headgear") that cites back into this family.
• The unrelated EP 3 994 020 ("A fuel gas system for a vehicle") is a different numbering system and a different invention; I have not substituted it.
• The 83 "Cited By" entries and the 6 foreign family members are forward citations/equivalents, not §102 art against '020.

Bottom line: On the retrieved data, the only U.S. patent documents cited on the face of US 3,994,020 are US 3,462,763 (Schneider et al., Aug. 1969), US 3,600,714 (Cade et al., Aug. 1971), and US 3,906,546 (Gooding, Sept. 1975), with a possible fourth (Gooding, 1973) from a third-party aggregator. None of the three verified references appears, on the available information, to disclose the differential-hardness, aligned fluid-filled chamber pair that is the point of novelty in independent claims 1–4, 21 and 28, and US 3,906,546 additionally cannot qualify under §102(a) or (b) because it issued after the filing date. Full-text verification is required before any of this is stated as a §102 conclusion.

I'll try to pull the actual prior-art citation list for this patent, since the "Prior Art" section of the supplied page appears truncated.

Let me try to retrieve the actual "Patent Citations" / prior-art reference list from mirror sites.

I found a cited-references listing. Let me verify the full prior-art citation set (US and foreign) for this patent.

Obviousness Analysis — U.S. Patent No. 3,994,020 (35 U.S.C. § 103)

0. Scope, sourcing, and a flag on the "Prior Art section"

Instruction conflict I must flag. The task says to "use the results from the Prior Art section of this page." The Google Patents text supplied as authoritative for this patent does not contain an intact prior-art citation block. What it contains is (a) machine-extracted "Prior art keywords" (liner, helmet, shell, liners, wearer), (b) a forward-citation table ("Cited By (83)"), and (c) a truncated "Families Citing this family (6)" list. The "Citations / Patent Citations (backward)" block was cut off in the fetch.

I therefore reconstructed the face citations from a mirror (Justia), and I must be explicit that my prior-art universe for this analysis is only three U.S. references, which is unusually thin for a §103 opinion:

Sources: https://patents.justia.com/patent/3994020 (Referenced Cited); https://www.freepatentsonline.com/CCL-2-413-p4.html (US 3,600,714 "HYDRAULIC HELMET" abstract); http://www.everypatent.com/comp/pat6226801.html (Cade's bladder described as "a centrally disposed sump and valve connected to front, rear, and side extensions… a multiplicity of connecting cells… filled with a hydraulic liquid"); https://www.freepatentsonline.com/D838922.html (3,600,714 "HYDRAULIC HELMET" / 3,462,763 "IMPACT ABSORBING PROTECTIVE HEADGEAR"); https://uspto.report/patent/grant/[3994021](/patent/3994021) (sibling, cites Cade '714 and Dunning '959).

A second flag with real legal consequence: US 3,906,546 issued Sep. 30, 1975 — after the '020 filing date of June 5, 1975. It can only have been cited as pre-AIA §102(e) art on the strength of its earlier filing date. §102(e) art is combinable for §103 (pre-AIA §103(a)), so I treat it as available conditionally — conditional on verifying its serial/filing date from the file wrapper, which I could not do here. Do not auto-correct this timing point.

Not available as prior art (and I will not use them as such): the same-day Kendall siblings US 3,994,021 and US 3,994,022, and US 4,062,068. They share the June 5, 1975 filing/priority and a common assignee and published the same day; they are evidentially useful only as context for how crowded the field was.

Legal posture. US 3,994,020 expired (anticipated expiration 1993‑11‑30) and cannot now be invalidated. This is therefore a retrospective §103 analysis: its real utility is (i) assessing the weight/teaching quality of the '020 disclosure where it is later cited as prior art, and (ii) reconstructing what the examiner likely faced. The governing framework is Graham v. John Deere (scope/content of art; differences; PHOSITA level; secondary considerations) as refined by KSR Int'l v. Teleflex (predictable variations, known techniques, design incentives, "obvious to try"), applied as of June 1975.

1. Person having ordinary skill in the art (PHOSITA)

A mechanical or protective-equipment engineer with ~2–4 years in athletic/crash-headgear design in 1975, who: knows rigid thermoplastic/polycarbonate and thermoset shells; is familiar with closed-cell foam liners (the '020 specification itself names Ensolite, Rubatex, and the De Cello rubber/PVC foam); knows inflatable bladders used for helmet sizing and the accessibility of inflation valves; and is aware of the emerging drop-test/accelerometer protocols — which the '020 specification expressly describes as the state of the art in its own Background. This PHOSITA is expected to be familiar with NOCSAE-style football-helmet impact standards (first NOCSAE football standard, early 1970s) — i.e., under a genuine, externally imposed incentive to raise measured energy attenuation. [Confidence: high on the general background; moderate on precise NOCSAE dates.]

2. Scope and content of the prior art

US 3,600,714 (Cade et al.), "Hydraulic helmet." Discloses three stacked elements: an outer (resiliently deformable) shell; an inner compressible liner contacting the user's head; and an intermediate bladder between the liner and the shell containing a multiplicity of connecting cells filled with hydraulic liquid, with a centrally disposed sump and valve and front, rear, and side extensions. On impact the liquid is displaced from the impacted cells into adjacent cells and the sump; the volume of liquid also adjusts fit (EveryPatent, quoting Cade: "it can be adjusted to a limited extent to accommodate various head sizes by changing the size of the cells through an increase or decrease in the amount of fluid placed in the cells"; https://www.freepatentsonline.com/CCL-2-413-p4.html).

What Cade supplies against the '020 claims: shell + liner means inside it for absorbing impacts; wall means of flexible material defining a plurality of fluid-filled chamber means lying intermediate head and shell; a plurality of fluid-filled compartments arranged radially about a central reservoir with a valve; a layered head-soft/shell-hard arrangement (its soft compressible liner inboard, its bladder outboard); and an explicit size-adjustment-by-fluid-volume teaching — the very fitting function the '020 claims as a "feature."

What Cade lacks: (i) wall portions of the cells having different hardnesses; (ii) the stacking of two fluid-filled chambers on the same head-to-shell axis (Cade's cells are laterally distributed, not nested/aligned pairwise); (iii) explicit durometer/modulus numbers; (iv) a crown opening through the liner (its sump is a reservoir, not an aperture).

US 3,906,546 (Gooding, 1975) and US 3,462,763 (1969). Both are impact-absorbing/energy-absorbing protective-headgear patents in the identical field and are the classic vehicle for a multi-layer or dual-characteristic liner teaching (a soft, skin-comfortable inboard layer plus a stiffer outboard energy-absorbing layer). I cannot verify their detailed disclosures in this session and I am not going to assert specific sentences from them. Treated below as generic "dual-characteristic liner" art; a full opinion would quote their claims/specification.

Admitted art within the '020 specification itself (highly probative, non-hearsay admissions by the applicant). The Background:

• "If the inner portion of the helmet which contacts the wearer's head is too hard, the wearer may suffer headaches or other discomfort" → admission that a soft head-contacting inner surface was a known design requirement, i.e., the motivation for the "soft inner liner" limitation is conceded to pre-date the invention.
• The drop-test/accelerometer discussion → admission that measured energy attenuation across a range of impact severities was the recognized problem to be solved.
• The FIG. 10 retainer pad 70′ — a single pad having a soft inner section 78 and a stiff outer section 80 of different foam compositions — is the applicant's own embodiment of the "soft-inside/hard-outside" principle. That the same applicant applied that principle to pads shows it was within routine design reach for the liners.

3. Claim-by-claim analysis

Legend for grounds:

• G1 = Cade '714 in view of dual-characteristic-liner art (Gooding '546 and/or '763), optionally + the admitted problem in the '020 Background.
• G2 = Cade '714 in view of the admitted soft-inner-liner requirement + routine material/hardness optimization (single-reference-plus-skill, In re Kotzab, In re Merck).
• G3 = Dual-characteristic-liner art + an inflatable-bladder/sizing reference (Cade '714; Dunning '959 is a further candidate — see §4 caveat).

4. Motivation to combine — articulated

The motivation in 1975 was not speculative; it is documented in the art and conceded in the patent:

1. A recognized, articulated problem with a known two-part answer. The '020 itself states the dilemma — comfort (soft head contact) versus protection (stiff energy management) — which is an admission of the problem and therefore supplies the "reason the inventor made the combination."
2. Two known, independently usable elements. (a) Fluid-filled multi-chamber liners for impact dispersal and fit adjustment (Cade; Dunning). (b) Graded/dual-characteristic liner stacks — soft inboard, stiff outboard — the standard foam-liner architecture (Gooding; the De Cello rubber/PVC foam material named in the '020; the applicant's own FIG. 10 pad 70′). Combining a known fluid-chamber layer with a known graded-stiffness stack is the combination of two known means, each performing its known function in the known way, to achieve a predictable cumulative energy-attenuation result (KSR).
3. Design incentive and regulatory pull. The drop-test/accelerometer framework described in the '020 Background and contemporaneous helmet impact standards gave every designer an incentive to add a second, higher-threshold energy-absorbing stage — i.e., to make the outboard chamber less deformable.
4. Fit remains intact. Because Cade's fluid-volume adjustment already solved multi-size fitting, adding a second, harder chamber does not defeat the fitting function — removing the classic "teaching away" defense that a combination would sacrifice adjustability.
5. Manufacturing simplification cut the other way. Producing the two portions in a single dual-durometer molding (claims 1–3) is the obvious fewer-parts variant of nesting two liners — an independent, adequate §103 rationale.
6. No teaching away and no criticality: nothing in the cited art disparages stacking fluid chambers, and the '020 supplies no comparative data showing the recited ranges or the specific nesting order produce unexpected results.

Weakness in the "different hardnesses" element. The single most forceful non-obviousness argument available to a defender of claim 1 is that neither Cade nor a foam-liner reference discloses two stacked fluid-filled chambers with wall portions of differing hardness, and that the prior art's soft/stiff distinction lived in foam, not fluid chambers. That argument is defeated only by clear evidence in the art that (a) inflatable liners themselves were known to be made in soft and stiff versions, or (b) dual-durometer single-piece hollow moldings were known. That is the evidentiary gap to close — see §5.

5. What a complete opinion would require (and what I could not verify)

• The complete "References Cited" list on the '020 face (my three-reference universe is incomplete — the page's citation block was truncated in the supplied text).
• The full '020 file wrapper (paper-era): the examiner's §103 rejections, the applicant's remarks/affidavits (e.g., Rule 132 comparative drop-test data), and the reasons for allowance. This is the single most probative document and I have not seen it.
• The drawings and full texts of Cade '714, Gooding '546, and '763, to test the claim-24 anticipation risk and to locate quotable dual-durometer / dual-layer teachings.
• Filing dates for Gooding '546 (to confirm its §102(e) availability, since it published after the '020 filing).
• Resolution of the inventor-name conflicts for '763 (Schneider et al. vs. Gooding) and '714 (Cade et al. vs. Greathouse). I have not auto-corrected or silently harmonized these.
• Contemporaneous non-patent art: NOCSAE draft/standard documents, RTI/industry helmet studies, and 1970s helmet-design literature, to establish PHOSITA background and the regulatory incentive.

6. Conclusion

On the record available, claims 1–4, 7–28 are, in my assessment, more likely than not obvious under §103 over Cade '714 in view of dual-characteristic/impact-absorbing-liner art (Gooding '546 and/or '763) and the admitted state of the art in the '020 Background — with the strongest individual showings being:

• Claims 5–6, 11–12, 16–19, 27–28 — routine optimization, known materials, known manufacturing methods, no criticality data;
• Claims 13–15 and 24–26 — closest to the art and carrying a genuine §102(b) anticipation risk if Cade's central sump defines a through-aperture, which I could not confirm;
• Claims 1–4, 21–23 — the crux (two stacked fluid chambers of differing hardness); obvious under KSR's predictable-variation and known-technique rationales, but this is where a well-funded patent owner's best counterargument lies, and it is decided on evidence I have not been able to retrieve (Cade's figures; the file wrapper; any dual-durometer bladder art).

I want to be explicit about the limits of this opinion: it rests on a reconstructed, three-reference prior-art set because the "Prior Art section" of the supplied page was truncated, and I have flagged two inventor-name conflicts and one dispositive date issue rather than resolving them. Treat the obviousness conclusions above as a well-grounded working hypothesis, not a definitive legal conclusion.