US 5815846

I'll search for the specific patent number and any related litigation docket activity.

Let me check for any litigation or CAFC docket activity involving this patent.

Search scope and limits (stated up front)

I searched for the exact string "5815846" (and the formatted equivalents "5,815,846" / "US5815846"), together with assignee and inventor names, against patent databases and general web indexes. I did not get a direct query into USPTO PatentCenter, PACER, or the CAFC docket system. My CAFC/litigation-specific queries ("5815846" + litigation/CAFC/Federal Circuit; Tecno-Fluidos + lawsuit/infringement; Tecno-Fluidos + CAFC 2026 docket) returned zero results. I therefore cannot confirm or deny any 2026 CAFC activity involving this patent; the accurate statement is no docket or litigation record for US 5,815,846 surfaced in my searches. Treat absence of results as absence of evidence, not evidence of absence.

No similar patent numbers are reported below — everything here is tied to US 5,815,846.

Bibliographic data

Sources: https://patents.google.com/patent/US5815846A/en ; https://patentimages.storage.googleapis.com/df/da/04/510908e9bf4171/US5815846.pdf ; https://patents.justia.com/patent/5815846

Abstract (as issued)

An impact resistant helmet assembly in which a first material layer is coupled to a second material layer to define a gas chamber therebetween containing gas that provides impact dampening. A containment layer over the second material layer defines a fluid chamber containing a quantity of fluid. The fluid is a generally viscous gel structured to resist disbursement from an impacted region of the fluid chamber to non-impacted regions, thereby enhancing impact distribution and dampening.

Independent claims in plain language

Claim 1 — An impact resistant helmet assembly comprising: (a) a first material layer; (b) a second material layer positioned relative to the first to define a gas chamber between them; (c) gas in that chamber for impact dampening; (d) a containment layer defining a fluid chamber; (e) fluid in the fluid chamber, such that fluid at an impacted region is disbursed to non-impacted regions for enhanced impact distribution/dampening; and (f) — the point of novelty — the fluid containing granular particulate that both resists that disbursement (enhancing dampening) and lowers the fluid's density to reduce weight. Notably, claim 1's characterizing feature is the particulate, not the viscous gel; claim 1 does not require the containment layer to be "coupled to" the second material layer, and does not require equalization pockets.

Claim 19 — Same gas-chamber/fluid-chamber architecture, but the characterizing combination is: the fluid is a generally viscous fluid (resisting disbursement), the fluid chamber contains a plurality of equalization pockets each holding a fluid reservoir and compressible on impact to urge fluid toward non-impacted pockets, and the non-impacted pockets are structured to expand to receive the increased fluid. This claim expressly recites the containment layer being coupled to the second material layer.

Claim 22 — Same gas-chamber/fluid-chamber architecture, but with the broadest pocket recitation: at least one equalization pocket in the fluid chamber, containing a fluid reservoir, compressible on impact to urge fluid from the impacted region toward the non-impacted region for substantial dampening. No "coupled to" limitation and no viscous-fluid limitation.

Notable claim-drafting observations

• Claims 12 and 21 are substantively identical — both recite the "generally tapered configuration… tip… small surface area… lessens a translated force" limitation and both depend from claim 9. This duplication is real in the printed patent (confirmed in the Google Patents, FreePatentsOnline, Justia, and SumoBrain claim sets), not a transcription artifact. It appears to be a drafting/redundancy error, not a correction to be made.
• The dependent-claim ladder adds: gas introduction means to adjust inflation and fit (claim 2); air as the gas (3); viscous fluid/gel (4, 5); granular particulate (6); a filter layer in the fluid chamber (7, 8, 11, 20); equalization pockets and their expansion (9, 10); tapered/conical pocket geometry with the tip facing the wearer's head, invoking Pascal-type force-distribution rationale (12, 21); an anti-deformation element (e.g., polystyrene) at each pocket tip (13); pockets formed in the second material layer (14); mating recesses in the first material layer (15); and a resilient foam liner with openings receiving the pockets (16, 17), plus a rigid exterior shell (18).
• The specification states the anti-deformation elements are preferably polystyrene and that the particulate may be pulverized volcanic rock — materials detail worth noting for any claim-construction or prior-art analysis.

Family, prosecution, and cited art

• Family/related filings (all claiming the 1996-11-27 priority): WO1998025488A2 (filed 1997-11-26, "An improved resistant helmet assembly"), EP1058509A2 (withdrawn), AU5590998A (abandoned), JP2002509586A. The WO/EP/AU/JP member titles use "An improved resistant helmet assembly," slightly different from the US title.
• Prior art cited on the face of the US patent: US 3,668,704 (Conroy et al.), US 3,872,511, SU 1,355,230, DE 4024957 (Bauer), US 5,181,279 (Ross), US 5,336,703. (Small discrepancy across sources: the printed front page lists US 3,872,511 under "Nichols," while Google Patents lists its inventor as Larcher, Angelo C.; similarly US 5,336,703 is listed as "Chen" on the face page but Google shows Kanegafuchi Chemical Industry Co., Ltd. as assignee. I am not resolving these — flagging the inconsistency.)
• The patent has been cited as prior art in a long line of later helmet patents (e.g., US 5,950,244; US 5,956,777; US 6,530,092; US 9,570,389; US 9,027,447-family filings), and Google Patents reports it as part of the citation lineage for the MIPS, Brainguard, 6D Helmets, and VICIS families.

Uncertainty statement

• I have high confidence in the bibliographic data, abstract, claim text, and status above; these come from the patent's own front page/PDF and multiple consistent patent databases.
• I have no authoritative information on any 2026 CAFC appeal, district court case, or other post-issuance proceeding involving US 5,815,846, and my targeted searches found none. Given the patent expired for non-payment of maintenance fees in October 2002, live enforcement litigation in 2026 would be unusual, but I am not asserting that none exists.
• If a PACER/CAFC docket check is required, it must be run directly against those systems; my search layer did not reach them.

I'll search for litigation involving US patent 5815846 across patent litigation sources.

Let me search specific litigation resources for this patent.

Let me do a few more targeted searches on docket databases.

Litigation Search Results — US Patent No. 5,815,846

Bottom line: I found no record of any litigation involving US 5,815,846.

The patent (as identified)

• Patent No.: US 5,815,846 (literal number as searched)
• Title: "Resistant helmet assembly"
• Inventor: Rafael Calonge
• Assignee: Tecno-Fluidos, S.L. (Spain)
• Application No.: US 08/753,693
• Filed / Priority: 1996-11-27
• Granted: 1998-10-06
• Status: Expired – Fee Related (maintenance fees lapsed; patent expired 2002-10-06 for failure to pay maintenance fees)

Litigation findings

Across the sources searched (Google Patents family/litigation data, Justia/FreePatentsOnline/SumoBrain patent pages, and general litigation-oriented queries such as "5815846 litigation," "5815846 patent lawsuit defendant," and Tecno-Fluidos infringement searches), no district court, CAFC, PTAB, ITC, or PACER case was surfaced naming US 5,815,846.

Important caveats

1. Do not confuse this patent with similarly numbered ones. My searches returned hits for US 5,784,584 (TPL / Technology Properties Ltd.), litigated in E.D. Tex. (Marshall Div.) against ARM licensees, with an ARM non-infringement judgment on/about 2007‑09‑12. That is a different patent and is not US 5,815,846. I am excluding it per your instruction not to return results for similar numbers.
2. Absence of evidence ≠ evidence of absence. I did not obtain a direct hit confirming "zero cases" from a dedicated litigation database (e.g., Unified Patents portal, Docket Navigator, or PACER/RECAP full-text). My searches of those resources did not return usable records for this specific number — the query tools returned empty or non-responsive results. So I can state no known litigation was found, but I cannot affirmatively certify that none exists. A definitive check would require a direct Docket Navigator / PACER / CourtListener RECAP query on the exact number and on "Tecno-Fluidos."
3. Practical context supporting the negative finding: The patent expired in 2002 for non‑payment of maintenance fees, and the international family largely lapsed or was abandoned (WO1998025488A2 "Ceased"; AU55909/98 "Abandoned"; EP1058509A2 "Withdrawn"). A patent that lapsed in 2002 is an unlikely candidate for active assertion litigation, which is consistent with (though not proof of) the absence of found cases.

Recommendation

If you need a certified negative, run a direct Docket Navigator or CourtListener RECAP search on:

• Patent number: 5815846 (and 5,815,846)
• Party names: Tecno-Fluidos, Tecno Fluidos, Rafael Calonge

I can run those specific queries if you want me to continue — just confirm.

PTAB Proceedings — US 5,815,846 ("Resistant helmet assembly," Tecno-Fluidos, S.L.)

Proceedings overview

Total AIA trial proceedings on file: 0. The USPTO Open Data Portal returns no IPR, PGR, or CBM proceeding naming US 5,815,846 — zero active, zero claims invalidated, zero claims sustained, zero settled, zero institution denials. My independent web searches (PTAB docket reporting, petitioner/patent-owner names "Tecno-Fluidos" and "Calonge," and the patent number) surfaced no PTAB trial, no Federal Circuit appeal of any PTAB decision, and no reexamination certificate on the face of the record. The defensive posture this gives a defendant is unusual but favorable: there is no PTAB win to borrow and no § 315(e)(2) estoppel to worry about — but you very likely don't need one, because US 5,815,846 lapsed for non-payment of maintenance fees and has been expired since 2002-10-06.

Two record facts drive everything below:

• Status: "Expired - Fee Related." The legal events show a maintenance-fee reminder on 2002-04-23 and lapse under 37 C.F.R. § 1.362 recorded 2002-11-06 (effective 2002-10-06) — i.e., the 4th-year fee was never paid. The nominal term (20 years from the 1996-11-27 filing) would have ended 2016-11-27; in either case the patent has been dead for years.
• No post-grant challenge appears on the record. Practical reason: by the time the AIA created IPR/PGR/CBM in 2012, this patent was already lapsed, so no challenger had any incentive to file. Absence of PTAB activity here is not evidence that the claims are strong — it is evidence nobody had anything to gain by attacking an expired claim set.

Proceedings

None. There are no proceeding numbers to report, and I will not invent any. The structured ODP block controls, and it is empty; the web searches did not contradict it.

One flagged false positive (not a proceeding on this patent)

Search results returned a 2025 PTAB briefing in which Patent Owner CM HK defended "the '846 Patent" against a Samsung IPR petition (discretionary-denial arguments under Fintiv / § 325(d), papers dated 2025-08-18). That is a different patent. The brief's own priority recitation places it in a 2010–2017 family (provisional 61/292,558 filed 2010-01-06; continuation-in-part filed 2017-06-02; expiring November 2030). US 5,815,846 was filed 1996-11-27 and lapsed in 2002. Do not cite that CM HK/Samsung matter as precedent about this patent.

Also checked and found nothing

• Federal Circuit docket / CourtListener — no appeal involving US 5,815,846, Tecno-Fluidos, or Rafael Calonge in connection with a PTAB decision.
• Ex parte reexamination — no reexamination certificate and no reexamination-related legal event appears in the prosecution history.
• Related non-US family (AU 55909/98 abandoned; EP 1058509 A2 withdrawn; WO 98/25488 ceased; JP 2002-509586 A pending) — these are foreign counterparts with their own statuses and are outside PTAB jurisdiction.

Strategic summary

Claim status — nothing is CANCELED, nothing is SUSTAINED, everything is UNTESTED, and everything is EXPIRED. All 22 claims stand as issued. No IPR ever canceled claim 1 (or any other claim), and no IPR ever confirmed one. That distinction matters: the patent has never been adjudicated valid by the PTAB, so there is no "hardened by IPR" narrative a plaintiff can tell. The claims are simply old and unenforceable-by-lapse. If you are receiving demand letters citing claims 1, 4, 5, 9, 19, or 22 of US 5,815,846, the defect is not invalidity — it is that the patent lapsed on 2002-10-06 for failure to pay maintenance fees and its statutory term has long since run. There is no live right to assert.

Estoppel landscape — there is none. § 315(e)(2) estoppel attaches only to IPR/PGR petitioners and their privies. With zero AIA trials, nobody is estopped from anything, and no prior-art ground has been "used up." The practical consequence is the mirror image of the usual analysis: because the patent is expired, the entire prior-art/§ 102/§ 103/§ 112 toolkit remains fully available for whatever other, live patent in a modern helmet case may be asserted against you.

Pattern signals — none, and the reason is structural. No serial petitioner, no defensive aggregator (Unified Patents, RPX, etc.), no aggressive PTAB appeals by the patent owner. The owner of record is a small Spanish entity (Tecno-Fluidos, S.L.; assignment from Rafael Calonge recorded 1997-10-06), and the patent was dropped in the very first maintenance-fee window. Beyond validity, US 5,815,846 is now free to cite as prior art (priority 1996-11-27) — and it is in fact cited on the face of, or in the families of, several later helmet filings (e.g., Kinetica/Kineticshield, BrainGuard Technologies/Brainguard, and the US 2016/0258503 / US 10,228,036 "Impact diffusing apparatus" family). That is where the real value of this document now lies for a defendant.

Recommended next steps

1. If you are a defendant being asserted against US 5,815,846: the answer is not an IPR petition. Print the prosecution history and put the fee-lapse events in front of the plaintiff. The controlling record entry is: "PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362," effective 2002-10-06, recorded 2002-11-06 — see Google Patents US5815846A — Legal Events and FreePatentsOnline US 5,815,846. Any demand premised on the claims is premised on a lapsed patent; consider a declaratory-judgment counterclaim of non-infringement/non-liability or a simple Rule 11 / § 285 posture letter if the demand persists.
2. If you wanted PTAB relief anyway: it is not available on the merits. An expired patent cannot be the subject of an IPR directed at claims the petitioner no longer has standing to challenge, and there is no damages exposure to moot. Do not file. There are no trial-stage deadlines to diarize — no institution deadline, no oral hearing, no FWD due date — because no petition was ever filed.
3. If your real interest is freedom-to-operate against a different, live helmet patent: pivot the search. No proceeding exists here, so there is no FWD to quote and no disposition to link. The absence of PTAB activity on US 5,815,846 is, as the operating instructions note, "itself a signal" — but here the signal is that the patent was abandoned at the first fee date, not that it weathered attack.

Confidence and limits: I am highly confident there is no AIA trial proceeding on US 5,815,846, because the ODP block states so and independent searching found nothing to the contrary plus a clear economic explanation for the silence. I could not rule out the theoretical existence of a very old, unindexed paper filing (e.g., a pre-AIA inter partes reexamination requested in a window I have not separately docket-searched), so I flag that as the one unverified corner rather than asserting a negative with absolute certainty.

I'll verify the assignment record and check for any NPE-relevant activity before writing up the analysis.

Let me check for any litigation, NPE activity, or additional corporate records involving the assignee.

Ownership & NPE Analysis — US 5815846 ("Resistant helmet assembly")

Data provenance note: The authoritative source in this working file is the Google Patents legal-events mirror of the USPTO assignment record (https://patents.google.com/patent/US5815846/en). I attempted live cross-checks against USPTO Assignment Center / PEDS / ODP, but the searches returned only the patent front matter and citing documents — no separate assignment abstract, no litigation docket, and no NPE-directory hit. Findings below are therefore bounded by what the fetched record actually discloses. Where a field (notably correspondent of record) is not present in the retrieved data, I say so rather than supplying a name.

Inventors

• No co-inventors. Single-inventor Spanish-origin filing.
• Departure pattern check: Not determinable. The record shows one assignment (Calonge → Tecno-Fluidos), which is the standard inventor-to-employer transfer, not a departure signal. There is no evidence of any further inventor-to-third-party conveyance. No "all inventors exit within 12 months" precursor to a portfolio fire-sale — the fire-sale signal is simply absent because ownership never left the operating company.

Original assignee

Tecno-Fluidos, S.L. (Spain) — named on the granted patent and recorded as assignee at reel 008741/0772.

• Product embodying the claims: The specification describes a complete, buildable helmet (rigid exterior shell 85, gas chamber 40 with inflate/deflate valve 90, viscous-gel fluid chamber 50, equalization pockets 70). The disclosure is drafted in product-implementation terms, consistent with an operating company rather than a paper filer. However, I found no independent evidence of a commercial helmet shipped under the Tecno-Fluidos name — searches returned only patent literature, not product or retail records. Treat "shipped a product" as unconfirmed.
• Primary line of business: Inferred as protective headgear / helmet manufacture (Spain). Not independently verified beyond the patent record.
• Current status: Unknown. No bankruptcy, acquisition, or dissolution record surfaced. The patent (not the company) is definitively dead: Expired – Fee Related, with lapse events logged 2002-10-07 / 2002-11-06 / 2002-12-03 and effective lapse date 2002-10-06 (failure to pay maintenance fees, 37 CFR 1.362).
• Family collateral status (from the same record): EP1058509A2 withdrawn, WO1998025488A2 ceased, AU5590998A abandoned, JP2002509586A pending/active at last entry. The international family was largely abandoned — the opposite of a portfolio being groomed for assertion.

Assignment timeline

Only one assignment is recorded against US 5815846. There is no post-issuance assignment, no security interest, no merger, no change of name, and no license recorded. That is itself a clean finding: ownership stayed with the original operating assignee until the patent lapsed.

• 1997-08-26 (executed) / recorded 1997-10-06 — Reel 008741/0772
  • Conveyance: Assignment
  • Assignor: Calonge, Rafael (individual inventor)
  • Assignee: TECNO-FLUIDOS, S.L. (Spain)
  • Correspondent: Not disclosed in the retrieved record. The Google Patents legal-events entry preserves the reel/frame (008741/0772) and the assignment-of-interest caption ("ASSIGNMENT OF ASSIGNORS INTEREST … ASSIGNOR: CALONGE, RAFAEL") but omits the recording attorney/agent. I will not invent one. Note the recording was filed ~10 months after the 1996-11-27 filing date, which is a routine post-filing ratification of an employer-assignment, not a transfer to a third party.
  • Context: Inventor-to-employer assignment (initial ownership transfer at origination) — not an acquisition, fire-sale, or transfer-to-asserter.

No further recordings exist. Nothing to chain, nothing to cascade.

Timeline diagram

timeline
    title Ownership of US 5815846
    1996 : Filed by Rafael Calonge
         : Priority date 27 Nov 1996
    1997 : Assigned to Tecno-Fluidos SL
         : Reel 008741 frame 0772
    1998 : Patent granted 6 Oct 1998
    2002 : Lapsed for unpaid maintenance fees

NPE / troll-pattern signals

1. Shell-entity transfer — Not present. The sole post-origination step is the inventor→operating-company assignment (reel 008741/0772, executed 1997-08-26). No transfer to any "IP / Holdings / Licensing / Ventures" entity. No single-purpose LLC appears anywhere in the chain.

2. Known asserter in the chain — Not present. No assignee matches Acacia, Marathon, Intellectual Ventures, IPNav, Wi-LAN, Conversi 2.0/Mosaid, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, Document Generation Corp, or any Spangenberg entity. The only assignee ever recorded is Tecno-Fluidos, S.L. — a Spanish helmet company. No Unified Patents / RPX high-frequency-plaintiff hit surfaced.

3. Repeat correspondent across the chain — Unclear / not present. There is only one recorded assignment, so "recurrence" is untestable by definition, and the correspondent field is not present in the retrieved record. A single appearance would not be a finding even if the name were available (many firms do both NPE and operating-company work). No correspondent to cite.

4. Cascading transfers — Not present. One assignment in the patent's entire recorded life. No chained LLCs, no shared-address pattern, no <24-month sequence.

5. Pre-litigation transfer — Not present. No infringement suit naming US 5815846 was found. There is no litigation event for the chain to have been arranged around, and the last ownership event is dated 1997 — over a decade before any plausible modern assertion wave.

6. Bankruptcy fire-sale — Not present / unknown. No Chapter 7/11 record tied to Tecno-Fluidos surfaced, and no sale-of-patents event appears in the legal events. The patent simply lapsed for non-payment (effective 2002-10-06), which is not a fire-sale conveyance.

7. Privateering — Not present. No operating-company-to-NPE transfer exists in the record.

8. Defensive aggregator (anti-NPE) — Not present. Chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN. If anything, the patent was neutralized by abandonment — the family's EP/WO/AU members were withdrawn/ceased/abandoned and the US patent lapsed in 2002 — but that is an expiry event, not a defensive-aggregator acquisition.

Verdict

Insufficient data (only the original assignment).

Justification: The complete recorded ownership history of US 5815846 is a single assignment — Rafael Calonge to Tecno-Fluidos, S.L., executed 1997-08-26 and recorded 1997-10-06 at reel 008741/0772 — with no subsequent transfer, security interest, license, or change of name ever recorded. No shell entity, known asserter, repeat correspondent, or pre-litigation transfer appears, and no infringement action naming this patent was found; the patent then expired for failure to pay maintenance fees effective 2002-10-06, and its international siblings were withdrawn, ceased, or abandoned. Every NPE signal the framework asks about requires a post-issuance conveyance that simply does not exist here, so the correct call is an absence-of-evidence finding rather than an inference of clean ownership beyond the one reel/frame on file. Verification: search 5815846 at https://assignmentcenter.uspto.gov/ (and the reel/frame 008741/0772) to confirm the single recorded assignment and the absence of any later recording.

Caveats I am deliberately flagging rather than papering over: (i) the correspondent of record for reel 008741/0772 is not present in the data I could retrieve and I have not fabricated it; (ii) Tecno-Fluidos, S.L.'s current corporate status and whether it ever commercialized a helmet are unverified — I found patent literature only, no product or registry record; (iii) JP2002509586A was last listed as pending/active, so any post-2026 activity on that national member is outside what this record covers.

I'll verify the patent and pull details on each cited reference.

Now let me examine the remaining cited references.

Let me research the remaining three references (SU1355230A1, DE4024957A1, US5336703A).

Prior-Art Analysis — U.S. Patent No. 5,815,846

"Resistant helmet assembly"

1. Document verification

I searched by the exact number 5815846 ("US5815846", "US5815846A", "US 5,815,846") and did not return or substitute results for any similar-looking number. Source: https://patents.google.com/patent/US5815846/en ; https://www.sumobrain.com/patents/us/Resistant-helmet-assembly/5815846.html ; https://FreePatentsOnline.com/5815846.html ; https://patents.justia.com/assignee/tecno-fluidos-s-l

Drafting anomalies noted for the record (not corrected): granted claim 21 is a verbatim duplicate of claim 12 (both recite the tapered/conical equalization-pocket configuration); claim 1's preamble is phrased in method language ("To dampen and resist an impact force applied thereto, an impact resistant helmet assembly comprising:…"). In the WO publication the applicant is recorded as "TECNO-FLUID AMERICA, INC." and the inventor as "GALONGE, Rafael" — apparent transliteration variants of Calonge; I have not auto-corrected them.

2. Methodology and the key § 102 caveat

The six references below are the complete "Patent Citations" set of US 5,815,846. All are flagged as cited by the examiner. Every one is more than one year earlier than the 1996-11-27 filing date, so each is available under 35 U.S.C. § 102(b) (and the U.S. patents also under § 102(a)/(e)).

Important analytical caution: anticipation under § 102 requires that a single reference disclose each and every element of a claim, arranged as in the claim. As shown below, no one of these six references anticipates independent claims 1, 19 or 22. The references are primarily § 103 obviousness material, used in combination. The one reference with a genuinely arguable § 102 theory is SU 1,355,230 A1, and even that is a stretch. I state this explicitly rather than manufacturing an anticipation match for each reference.

3. The six cited references at a glance

4. Reference-by-reference analysis

4.1 US 3,668,704 A — Conroy et al., "Protective headgear"

• Full citation: US 3,668,704 A, Robert E. Conroy & John H. Hauger, "Protective headgear," Appl. No. 54,513, filed 1970-07-13, issued 1972-06-13 (CIP of Ser. No. 12,805 filed 1970-02-19, abandoned). 16 claims, 20 figures.
• Sources: https://patents.google.com/patent/US3668704 ; https://www.freepatentsonline.com/[3668704](/patent/3668704).html ; https://patentimages.storage.googleapis.com/99/37/f6/9b4839bda06452/US3668704.pdf
• Description: An inflatable T-shaped member mounted inside the curvature of a rigid shell, preferably inserted within a slightly oversized foamed-elastomeric envelope bonded to the shell interior. Air-fill means (an elongated fill tube with a friction-fit cap) let the user inflate a plurality of communicating compartments, both sizing the shell to the head and cushioning against shock. The cap can be designed to blow off at a predetermined pressure to relieve severe impacts.
• Claim mapping: The examiner's "field of search" for 5815846 (2/411–414, 2/425) overlaps this art. Conroy discloses the gas chamber + gas + user-adjustable inflation elements (claim 2's "gas introduction means," claim 3's air, claim 18's rigid exterior shell, and a foam layer akin to claim 16).
• § 102 position: No anticipation. Conroy contains no fluid chamber, no viscous gel, no granular particulate, and no tapered equalization pockets. It cannot anticipate claim 1 (or any claim depending from it) because those elements are absent. It is element-level support for an obviousness combination against claims 2, 3, 16, 18.

4.2 US 3,872,511 A — Larcher, "Protective headgear"

• Full citation: US 3,872,511 A, Angelo C. Larcher, "Protective headgear," filed 1974-03-11, issued 1975-03-25. (Improvement over Larcher's earlier US 3,787,893.)
• Sources: https://patents.google.com/patent/US3872511 ; https://FreePatentsOnline.com/[3872511](/patent/3872511).html ; https://www.sumobrain.com/patents/us/Protective-headgear/3872511.html
• Description: An outer protective covering spaced from a conventional helmet to house "a multitude of fluid chambers or cushions" over substantially the entire interior area, so the shock is absorbed/dispersed exteriorly of the helmet before reaching the hard shell. Each cushion is a hollow chamber with valve means — a normally open large fluid intake and a small fluid outlet — that is closed by the outer shell under substantial impact "so as to retard the collapse of the chamber," thereby spreading the full force over a wide area.
• Claim mapping: Relevant to claim 1's gas-chamber/fluid-chamber architecture, to claim 9 (multiple fluid-containing chambers compressed and communicating on impact) and claim 18 (rigid exterior shell).
• § 102 position: No anticipation. Larcher's fluid chambers are air-assisted chambers with valve-restricted flow; there is no gas chamber distinct from a fluid chamber, no viscous gel, and no granular particulate. Compare, however, the specification's own Background section, which criticizes prior art "air between various foam filled pockets" where the only resistance is "a size of the connections between the pockets" — that passage reads as an implicit characterization of art of the Larcher/Larcher-893 type and is worth weighing if obviousness is at issue.

4.3 SU 1,355,230 A1 — Soroka, "Crash helmet having multiple-layer structure" (Защитный шлем с многослойной структурой) — MOST MATERIAL

• Full citation: SU 1,355,230 A1, inventor Сорока Виктор Михайлович (Viktor Mikhaylovich Soroka); applicant Рижское высшее военное авиационное инженерное училище им. Я. Алксниса (Riga Higher Military Aviation Engineering School named after Ya. Alksnis). Filed 1985-05-23, published 1987-11-30. IPC A42B 3/02.
• Sources: https://patent.google.com/patent/SU1355230A1/en ; https://patenton.ru/patent/SU1355230A1 ; https://rusneb.ru/catalog/000224_000128_0001355230_19871130_A1_SU/
• Description (from the Russian text): The helmet has an outer elastic shell 1, an intermediate rigid shell 2 provided with valves 3, and an inner shell 5 connected to inner equipment, plus an additional deformable shell 6 between the intermediate and inner shells (middle variant). The space between the outer and intermediate shells and the space between the intermediate and additional shells are filled with liquid 4 / 8; the space between the additional and inner shells is filled with gas 7 (e.g., air or nitrogen). The liquid is specified as viscous — viscosity on the order of 3–30 cSt and specific weight ≈ 0.85×10³ N/m (example: transformer oil). On impact the outer shell deforms and drives the liquid through the valves 3 into the space between shells 2 and 6, compressing the gas-filled thin shell 6; when the gas-elastic force exceeds the liquid pressure the flow reverses. Impact energy is dissipated through hydraulic losses at the valves and heating of the liquid; the specification claims a 10–15× improvement in protective properties.
• Claim mapping: This is the closest cited art to the invention's core architecture — a gas volume and a viscous liquid volume separated by a shell, with valve-restricted liquid transfer between regions on impact and dissipation by hydraulic loss/heating. It maps onto claim 1's "gas chamber… fluid chamber… resistance against disbursement from said impacted region… to said non-impacted regions"; onto claim 4's "generally viscous fluid"; and onto claims 9/19/22's compressible, communicating fluid reservoirs.
• § 102 position: This is the only citation with a realistic (though still contestable) anticipation theory, and it is aimed at claim 22 — the broadest independent claim, which requires only one "equalization pocket" of fluid compressed on impact to urge fluid toward a non-impacted region. SU 1,355,230's valved liquid space behaves in that manner. It is not a clean § 102 hit, because (i) the liquid is not contained in a discrete "equalization pocket" as the claim's reservoir, (ii) the fluid layer sits outboard of the gas layer rather than the claim's arrangement, and (iii) the reference is entirely silent on granular particulate — which is a positive recitation of independent claim 1 and of claim 6, and therefore defeats anticipation of claims 1 and 6 outright. Its strongest role is as the primary § 103 reference against claims 1, 4, 9, 12, 19 and 22.

4.4 DE 40 24 957 A1 — Bauer, adaptable liner for a motorcycle helmet

• Full citation: DE 40 24 957 A1, Willy Bauer, filed 1990-08-07, published (Offenlegungsschrift) 1992-02-13. Classified in the 5815846 record at 2/411.
• Sources: as listed in the 5,815,846 citation table and SumoBrain's domestic/foreign reference list for US 5,815,846 (https://www.sumobrain.com/patents/us/Resistant-helmet-assembly/5815846.html).
• Description (per the record's title/abstract line): "Adaptable liner for motorcycle helmet — comprises gel cushion layer and variable profile layer filled with air or gel which is pumped in from reservoir."
• Claim mapping: Directly relevant to claim 5 ("said fluid includes a generally viscous gel"), claim 4 (viscous fluid), and claim 2 (adjustable gas introduction) — it discloses a gel cushion layer alongside an air/gel-filled variable-profile layer supplied from a pump and reservoir.
• § 102 position: No anticipation. Even at the element level the reference, as characterized in the record, describes a gel layer and a pumpable layer, but not the claimed fluid-chamber-with-granular-particulate or the equalization-pocket geometry. It is the natural § 103 companion to SU 1,355,230 A1 for claims 4 and 5.
• Verification caveat: my independent full-text retrieval of DE 40 24 957 A1 was cut short by a tool step limit this session. The description above reflects the citation record furnished with US 5,815,846 plus one secondary listing; it should be re-verified against the DE full text (https://patents.google.com/patent/DE4024957A1/en) before being relied on.

4.5 US 5,181,279 A — Ross, "Cushioned helmet"

• Full citation: US 5,181,279 A, Dale T. Ross, "Cushioned helmet," Appl. No. 07/797,379, filed 1991-11-25, issued 1993-01-26. Primary class 2/413; IPC A42B 3/12.
• Sources: https://patents.google.com/patent/[US5181279A](/patent/US5181279A) ; https://FreePatentsOnline.com/[5181279](/patent/5181279).html ; http://www.everypatent.com/comp/pat5181279.html ; https://worldwide.espacenet.com/publicationDetails/claims?CC=US&NR=[5181279A](/patent/5181279A)
• Description: A rigid full-face shell with a cushion outer lining coextensive with the shell interior and an inner lining spaced from it to define a pneumatic chamber coextensive through the interior; a pump bladder on the exterior for selective pressurization and a pressure-release valve diametrically opposed to it; a sensor bore with a pressure transducer and display; and a row of "U"-shaped foam cushion inserts seated against the inner lining to accommodate different head sizes.
• Claim mapping: Claim 2 (gas introduction means varying fit and dampening), claim 3 (gas includes air), claim 16 (resilient material layer between the layers and the head), claim 18 (rigid exterior shell). Its own "References Cited" (Conroy 3,668,704; Villari 3,994,020; Jencks 4,035,846; Halstead 5,083,320; etc.) confirms the crowdedness of the art.
• § 102 position: No anticipation. No fluid chamber, no viscous gel, no granular particulate, no equalization pockets. Element-level § 103 material only.

4.6 US 5,336,703 A — Kanegafuchi Chemical Industry Co., Ltd., curable composition

• Full citation: US 5,336,703 A, "Two pack type curable composition comprising epoxy resin and silicon-containing elastomeric polymer," assignee Kanegafuchi Chemical Industry Co., Ltd.; priority/filing 1988-11-25, issued 1994-08-09. (The SumoBrain reference list for 5,815,846 records this document in the same class field, 2/411, and attributes it to "Chen.")
• Sources: the citation tables at https://www.sumobrain.com/patents/us/Resistant-helmet-assembly/5815846.html and https://patents.google.com/patent/US5815846/en
• Description: A two-part (two-pack) curable polymer composition combining an epoxy resin with a silicon-containing elastomeric polymer — i.e., a curable elastomer/gel chemistry reference, not a helmet reference.
• Claim mapping: Solely a materials citation, evidently relied on for the "generally viscous gel" limitation of claims 4, 5 and 6. It discloses no helmet structure whatsoever.
• § 102 position: No anticipation of any claim — it cannot disclose the helmet assembly elements, so it cannot satisfy the "arranged as in the claim" requirement for any of claims 1–22. It is a § 103 secondary reference only.
• Verification caveat: as with DE 40 24 957 A1, full-text retrieval of US 5,336,703 A was cut short by a step limit; the description above is drawn from the citation record and one secondary listing and should be re-verified (https://patents.google.com/patent/US5336703A/en).

5. Family/related citations worth noting (not among the six)

• US 5,336,708 A, Applied Elastomerics, Inc., "Gelatinous elastomer articles" (priority 1977-03-17; issued 1994-08-09) — listed in the 5,815,846 record as a "Family Cites Families" reference. Like US 5,336,703 A, it is a gel-material citation supporting the viscous-gel claims (4–6), not a structural reference.
• Cited-by art that is useful for later-claim context: US 5,950,244 A (Sport Maska, "Protective device for impact management," 1999), US 5,956,777 A (Grand Slam Cards, "Helmet," 1999), US 6,530,092 B2 (Southern Impact Research Center, inflatable liner fitting/comfort system, 2003), and US 2012/0204329 A1 / US 9,572,389 B2 (Kinetica/Kineticshield, fluid-filled containers and force-minimization structures).
• Also directly relevant text from the same inventor family: WO 98/25488 A2 / EP 1,058,509 A2 / AU 55909/98 A / JP 2002-509586 A, all claiming the same 1996-11-27 priority.

6. Conclusions

1. No cited reference anticipates claims 1 or 19. Independent claim 1 positively recites "a plurality of granular particulate disposed therein … structured to lower a density of said fluid so as to lessen a weight thereof." None of the six cited references discloses granular particulate in a helmet fluid chamber. That limitation alone defeats § 102 for claim 1 and for claims 2–18 as dependent thereon. Claim 19's combination (viscous fluid + multiple equalization pockets + expansion of non-impacted pockets) is likewise unmet by any single reference.
2. Claim 22 is the exposed claim. It omits the granular-particulate and viscous-fluid limitations and requires only one compressible equalization pocket urging fluid toward a non-impacted region. SU 1,355,230 A1 is the reference to press here, though on the Russian disclosure it is a stronger § 103 than § 102 case because of the discrete-pocket and layer-ordering differences.
3. SU 1,355,230 A1 is the most relevant single reference overall — it alone discloses a helmet with both a gas-filled space and a viscous liquid (transformer oil, ~3–30 cSt) space, with valve-restricted liquid transfer and energy dissipation by hydraulic loss and fluid heating. It is the closest thing in the record to the 5,815,846 architecture and would be the primary reference for any obviousness challenge to claims 1, 4, 9, 12, 19 and 22.
4. US 3,668,704 A and US 5,181,279 A supply the "adjustable gas chamber / gas introduction means / air" elements (claims 2–3) and the resilient/foam liner and rigid-shell elements (claims 16, 18).
5. US 3,872,511 A supplies multiple fluid chambers compressed on impact with valve-restricted flow (claims 9, 10).
6. DE 40 24 957 A1 supplies the gel-layer + pumpable-layer teaching for claims 4–5.
7. US 5,336,703 A (and US 5,336,708 A) are material/chemistry citations only, relevant to the gel recitation of claims 4–6 and incapable of anticipating any claim.

7. Explicit limitations on this analysis

• I was able to retrieve and read full text for US 5,815,846, US 3,668,704 A, US 3,872,511 A, US 5,181,279 A and SU 1,355,230 A1. For DE 40 24 957 A1 and US 5,336,703 A, retrieval was truncated by a session step limit; the characterizations above rest on the citation record furnished with US 5,815,846 and one secondary listing and should be independently re-verified before reliance.
• I do not have the USPTO file wrapper (Office actions / examiner's reasons for allowance) for application 08/753,693. I therefore cannot state whether any of these six references was actually applied in a rejection or merely listed in an IDS. The "potential anticipation" statements above are my independent element-by-element assessment, not a record of what the examiner did.
• One discrepancy in secondary sources: SumoBrain's reference list for US 5,815,846 credits US 3,872,511 to "Nichols," while the authoritative patent text and Google Patents credit Angelo C. Larcher. Per the governing instruction, I have not auto-corrected it; I note it as a source error in the secondary listing.
• § 102 and § 103 are legal conclusions; nothing here is a legal opinion.

I'll ground my analysis in the cited prior art. Let me first verify the disclosures of the six references listed in the Prior Art section (plus the family-cited gelatinous elastomer reference).

Now the remaining cited references and the family-cited elastomer reference:

Obviousness Analysis of U.S. Patent 5,815,846 under 35 U.S.C. § 103

Patent under review: US 5,815,846 A, "Resistant helmet assembly"; inventor Rafael Calonge; applicant/assignee Tecno‑Fluidos, S.L. (Barcelona, ES); application US 08/753,693 filed 1996‑11‑27; granted 1998‑10‑06; expired‑fee‑related as of 2002‑10‑06 (maintenance fee lapse under 37 C.F.R. 1.362).
Source: https://patents.google.com/patent/US5815846/en

Governing framework: Because the application was filed before 16 March 2013, pre‑AIA § 103(a) applies. The analysis below follows the Graham v. John Deere factors (scope/content of the prior art; differences; level of ordinary skill; objective evidence) and the KSR Int'l v. Teleflex rationales (predictable combination of known elements; substitution of a known element; use of a known technique to improve a similar device in the same way; "obvious to try" where the prior art identifies a finite number of identified, predictable solutions).

Identifiers are reported exactly as they appear on the patent's own face and in its citation tables. Two inconsistencies in the record are noted and left uncorrected: the face of US 5,815,846 lists US3872511A as "Nichols" (Google's citation table lists "Larcher Angelo C"), and lists US5336703A as "Chen" (Google's citation table lists assignee "Kanegafuchi Chemical Industry Co., Ltd."). Neither discrepancy affects the substance below.

1. References of record (all § 102(b) art)

All references published more than one year before the 1996‑11‑27 filing date and are therefore § 102(b) prior art available for § 103 combination.

2. Level of ordinary skill in the art (LOOS)

A person of ordinary skill in this art at the 1996 critical date would have (a) a bachelor's degree in mechanical engineering, materials science, or a comparable discipline, or (b) several years of practical experience designing protective headgear, and would be familiar with the conventional toolkit then in use: rigid shells, expanded polystyrene (styrofoam) foam liners, inflatable/pneumatic bladders with check valves, and hydraulic/gel liners with throttled or valved fluid passageways. Critically, all four of the US/foreign references are classified in Class 2, subclasses 411–414 or 2/425 and in IPC A42B3/12 (helmet cushioning devices, fluid‑containing pads) — the same classification assigned to US 5,815,846. That mutual classification is itself objective evidence that these are the same field of endeavor and the same problem space.

3. Claim 1 — the layered gas/fluid architecture is fully taught; the granular particulate is the only genuine gap

Claim 1 requires: (i) first and second material layers defining a gas chamber with gas for dampening; (ii) a containment layer defining a fluid chamber; (iii) fluid that disburses from an impacted region to non‑impacted regions; and (iv) granular particulate in the fluid, providing resistance to disbursement and lowering fluid density to reduce weight.

Primary combination: SU1355230A1 as the base reference, in view of DE4024957A1 and US5181279A / US3668704A.

Result: Elements (i)–(iii) of claim 1 are squarely disclosed by SU1355230A1, which teaches a helmet in which a gas‑filled layer and one or more liquid‑filled layers coexist, a viscous liquid is deliberately chosen, and impact energy is dissipated by hydraulic losses (throttled valves) plus fluid heating. DE4024957A1 independently teaches the same dual‑media architecture in a helmet liner (an air/other‑substance chamber plus a gel chamber) and adds the pump‑and‑valve volume adjustment. The only unmet limitation is the "plurality of granular particulate."

That gap is analytically important: claims 1–18 and 21 all carry the granular‑particulate limitation (claim 1 recites it; claims 2–18 depend from claim 1; claim 21 depends from claim 9, which depends from claim 1). Claims 19, 20 and 22 do not.

Can the gap be closed? Not on the four corners of these six references. However, a KSR‑style case is available and should be stated candidly as requiring an additional evidentiary basis:

• Adding lightweight solid fillers to a working fluid to reduce overall weight is a notoriously well‑known engineering expedient (weight reduction of liquid/gel‑filled liners was a recognized design constraint, and the patent's own stated object is a "substantially light weight" helmet).
• US 3,849,801 and US 4,375,108 — not of record here — disclose hydraulic helmet liners in which the fluid‑containing compartments are substantially filled with reticulated open‑cell foam inserts functioning as "surge mitigating" means that impede and throttle fluid flow between compartments. That is the same functional concept (a lightweight, flow‑impeding solid occupying the fluid volume) achieved by a different physical form, and it is the closest thing in the art to the claimed particulate. But because these are not among the references of record and because a foam insert is not literally "granular particulate," this route requires either an additional reference or an express "known technique/obvious to try" rationale buttressed by evidence of what a POSITA would have understood. I would not represent claim 1 as clearly obvious on the present record.

4. Claims 19 and 22 — the strongest § 103 candidates (they do not require granular particulate)

Claim 19

Claim 19 = layering + gas chamber + gas + containment layer coupled to the second layer defining a fluid chamber + viscous fluid resisting disbursement + plurality of equalization pockets, each holding a fluid reservoir, compressible on impact to urge fluid to non‑impacted pockets, with non‑impacted pockets expanding to receive it.

Combination: SU1355230A1 + US3872511A (Larcher), optionally with DE4024957A1.

• SU1355230 gives the gas/liquid layer stack, the gas chamber, and the viscous liquid whose energy dissipation depends on resistance to flow ("энергия удара расходуется на гидравлические потери в клапанах 3 и на нагрев жидкости" — impact energy is consumed by hydraulic losses at the valves and by heating of the liquid).
• Larcher gives the multiplicity of discrete fluid chambers ("a multitude of fluid chambers or cushions") arrayed over the helmet interior, each with valve means that retard the collapse of the chamber — i.e., each chamber holds a reservoir of fluid and, when compressed by an impact, is throttled so that its fluid is expressed into the surrounding space. Larcher also expressly states the object of disbursing the impact force over a wide area, which is the functional core of the "equalization pocket" concept.
• DE4024957 supplies the express plurality of sub‑divided chambers within one liner (labyrinth welds creating discrete cells) and confirms that the cells of a multi‑media liner may be expanded/contracted in volume.

Motivation: all three address the same problem the '846 patent identifies — that a non‑standard head leaves gaps that produce localized pressure peaks and prevent even energy distribution. SU1355230 states that a standard helmet shape does not match any wearer; DE4024957 states that the resulting gaps "lead to pressure peaks... and prevent an even energy distribution," and that a gel‑filled variable‑distance compensator supplies "high shock‑absorption properties." Combining a valved liquid layer (SU) with discrete, throttled chambers (Larcher) and a gel‑filled, variable‑volume chamber (DE4024957) is a combination of known elements in the same field, with predictable results.

Claim 22

Claim 22 requires only "at least one equalization pocket... containing a reservoir of said fluid... structured to be compressed upon the impact force... so as to urge said reservoir... towards said non‑impacted region."

This is the narrowest and most vulnerable claim. Larcher's chamber‑with‑throttling‑valve reads directly on it: each cushion is a fluid reservoir that, on impact, is compressed and expresses its fluid through a small outlet (with the large intake closed by the deforming outer shell) so that the fluid is urged outward rather than being trapped. Combined with SU1355230's gas chamber, every element of claim 22 is present. Claim 22 would, in my view, be the claim most likely to fall.

5. Dependent claims — element‑by‑element obviousness

6. Why a POSITA would have combined these references

1. Same field, same problem. Every reference is directed to impact‑attenuating headgear, classified (where classified) in Class 2/411–414, 2/425 and/or IPC A42B3/12 — the same art as the '846 patent. The problem addressed (distributing impact energy and fitting a non‑standard head) is identical.

2. The multi‑media, layered liner was itself a known concept. SU1355230A1 already places a gas‑filled layer adjacent a liquid‑filled layer in one helmet; DE4024957A1 already places an air (or other substance) chamber adjacent a gel chamber in one helmet liner. Thus the claimed "gas chamber + fluid chamber" stack is not a novel architectural insight but the combination of known elements according to known methods, yielding predictable results (KSR rationale 1). The applicant's own specification concedes the existence of air‑pocket and foam liners in the art.

3. Substitution of a known fluid for a known fluid. Replacing or supplementing a pneumatic chamber (Ross, DE4024957) with a viscous liquid/gel chamber (SU1355230, DE4024957) is the substitution of one known element for another to obtain its known advantage — resistance to flow that translates more of the impact force into fluid motion (KSR rationale 2).

4. Known technique, same way, similar device. Using throttling structure (valves with restricted outlets, labyrinth welds, restricted inter‑pocket connections) to slow fluid displacement is a known technique applied in Larcher and SU1355230 to improve a similar device in the same way — dissipating more impact energy per unit time (KSR rationale 3).

5. Both architecture references are "ready for improvement." DE4024957 expressly frames its liner as solving the gap/localized‑pressure problem and expressly provides pump/valve adjustability; SU1355230 expressly reports a 10–15× improvement from its multi‑layer liquid/gas scheme. Both are tailored to the very purpose recited in the '846 claims (KSR rationale 4).

6. No teaching away. None of the references disparages combining a gas layer with a fluid layer; SU1355230 affirmatively teaches it, and DE4024957 affirmatively teaches gel + gas in a single liner. The '846 patent's own criticism of the prior art is directed at uncontrolled air movement between foam pockets, which the cited throttling structures (Larcher's small outlet; SU's valves; DE4024957's labyrinth cells) already address — and that criticism, being an admission about the art, works against the patent, not for it.

7. Reasonable expectation of success. Each component (foam liner, inflatable bladders, valved fluid chambers, gel pads) had been used in helmets for two decades or more. Layering them and tuning flow restriction produces an additive, predictable damping result.

7. Where the § 103 case is weak — candid assessment

• Granular particulate (claims 1–18, 21). This limitation is not disclosed in any of the six references of record, nor in the family‑cited gelatinous‑elastomer reference, nor in the composition reference cited on the face. It is the load‑bearing difference for the entire dependent‑claim set. It can be attacked by (i) a KSR "known lightweight filler / obvious to try" rationale, and (ii) the reticulated‑foam‑in‑hydraulic‑compartment art (US 3,849,801; US 4,375,108), but neither is clean: the foam references disclose a foam body, not granular particulate, and are not references of record. This is the point at which an invalidity contention is most likely to fail.
• Claim 15 (recessed/mating regions) and claim 12/21 (tapered tip + small surface area). These are geometry/design‑choice limitations supported mainly by inference from the references' stated objectives rather than by express disclosure. They are maintainable arguments for patentability, though weakened by the fact that the claimed advantage (less force transmitted through a small area) is asserted in the specification as a consequence of Pascal's principle rather than as an unexpected result.
• Objective evidence. No evidence of commercial success, long‑felt need, failure of others, or copying has been presented here. If such evidence exists and has a nexus to the claims, it would need to be weighed; none is available in the record supplied. Likewise, the record contains no evidence that any reference teaches away from the claimed combination — if anything, SU1355230 teaches toward it.
• Legal status. The patent expired on 2002‑10‑06 for nonpayment of maintenance fees. A § 103 challenge today would be relevant chiefly to (a) related family members — e.g., JP 2002‑509586 A, which remains listed as pending/active — or (b) defensive/preclusion purposes. Note also that reexamination premised solely on art already considered by the examiner (all six references were on the face) faces a higher hurdle in establishing a substantial new question of patentability; the SNQ would have to rest on the new combinations and new rationales set out above rather than on the bare references.

8. Bottom line

Overall: US 5,815,846 claims a layered helmet liner whose gas‑chamber/gel‑chamber architecture, viscous‑fluid damping by resisted flow, and inflatable fit adjustment were each squarely disclosed before the 1996 filing date — most notably by SU1355230A1 (gas layer + viscous liquid layers + dissipative valves in one helmet) and DE4024957A1 (air chamber + gel chamber, pump/valve adjustable, expressly for even energy distribution). The claim set's genuine point of novelty, and therefore the pivot of any § 103 challenge, is the recited plurality of granular particulate in the fluid — a limitation that the prior art of record does not disclose, so that the obviousness case is strongest for independent claims 19, 20 and 22 and weakest for claim 1 and its dependents.

This is a technical prior‑art analysis prepared from the references cited on the face of US 5,815,846 and from their publicly available texts; it is not a legal opinion on validity or infringement, and it does not account for evidence of secondary considerations, which would have to be weighed if presented.

Key source URLs:

• https://patents.google.com/patent/US5815846/en
• https://www.sumobrain.com/patents/us/Protective-headgear/[3872511](/patent/3872511).html
• https://patenton.ru/patent/SU1355230A1 (and https://rusneb.ru/catalog/000224_000128_0001355230_19871130_A1_SU/)
• https://patents.google.com/patent/DE4024957A1/en
• https://patents.google.com/patent/US5181279A/en and https://www.freepatentsonline.com/[5181279](/patent/5181279).html
• https://www.freepatentsonline.com/[3668704](/patent/3668704).html
• https://patents.google.com/patent/US5336708A/en (family‑cited gelatinous elastomer)
• Extra‑record, for the foam‑in‑hydraulic‑compartment point only: https://www.sumobrain.com/patents/us/Protective-gear-with-hydraulic-liner/[3849801](/patent/3849801).html and https://uspto.report/patent/grant/[4375108](/patent/4375108)