US 3042167

I'll run targeted searches for this specific patent number and any 2026 CAFC activity.

Now let me check for CAFC litigation/docket activity and assignment records.

Let me do two final confirmation searches on litigation and the official record.

US Patent 3,042,167 — "Friction Clutches" (US3042167A)

Bibliographic record

Source: https://patents.google.com/patent/US3042167/en ; https://insight.rpxcorp.com/patent/US3042167A ; https://www.freepatentsonline.com/CCL-192-85.38-p2.html

Note on assignee: the printed patent names Rolls-Royce Limited. Google Patents lists the "Current Assignee" as Rolls Royce PLC, which reflects the later corporate name (Rolls-Royce Limited was renamed Rolls-Royce plc in 1987), not a fresh assignment on the face of the document. I have not verified a recorded assignment chain in USPTO Assignment records directly.

---

USPTO / CAFC 2026 litigation check

• No 2026 CAFC docket, IPR, PGR, reexamination, or district-court activity involving US 3,042,167 was found. My searches surfaced only unrelated 2026 Federal Circuit matters (e.g., Ironburg v. Valve, 2024‑2088; Spero v. Mercedes‑Benz, 2025‑1306/1307/1470/1473) and unrelated Rolls‑Royce PTAB/litigation history (e.g., IPR2016‑00528, Rolls‑Royce v. UTC). None concerned this patent.
• This is consistent with the record: the patent expired July 3, 1979, so it is long outside any IPR/PGR window (35 U.S.C. §§ 311(c), 321(c)) and has no live infringement exposure.
• Caveat: I relied on web search, not a direct docket query. I could not retrieve a live PatentCenter/PTAB or CAFC docket page tied to this number, and the last search step was cut off. Treat "no litigation" as a high-confidence but search-derived conclusion.
• False-positive warning: Google Patents' "Cited By" list for this patent includes three Centripetal Networks network-security patents (US 9,413,722; 9,560,176; 9,686,193) and an unrelated EP publication number "3042167 MULTIBRID GMBH" also appeared in search. These are artifacts/unrelated documents, not citations to this patent.

---

Abstract

This is a pre-1963 US patent and therefore has no formal "Abstract" on its face. The closest functional equivalent is the "Definitions"/summary language Google Patents extracts, which restates the invention's core point: the fluid-actuated piston-and-cylinder device is connected to one of the rotating drive members, so centrifugal force raises the operating-fluid pressure — and the device is formed so that the opposite faces of the piston have equal effective area, balancing those centrifugal pressure effects across the piston.

Disclosure overview (brief)

A multi-plate friction clutch between a gas-turbine engine and an auxiliary compressor rotor. A rotating cylindrical casing (27, the input drive member) carries splined clutch plates (31); the output shaft (24) carries alternate plates (33), pressed by a movable thrust plate (35) on a sleeve/skirt assembly (36, 37) whose web forms a double-acting piston (38). Low-pressure oil (backing pump 64, ~50 psi) permanently fills chamber (56); high-pressure oil (pumps 64+66, >400 psi) fills chamber (60) when a two-position valve (68) connects line 67 to line 71; venting line 71 to return line 70 disengages. Low-pressure oil also wets the plates via drillings (61, 62). Because piston faces have equal effective area, centrifugal pressure rise in the rotating chambers is balanced and does not spuriously disengage the clutch. Contextual application: a rotary-wing/tilt arrangement in which a turbo-propeller engine's low-pressure turbine drives the compressor that supplies air for the rotor's motive fluid.

---

Independent claims in plain language

Claim 1 — A friction clutch with an input drive member and an output drive member, each carrying at least one friction drive element movable into/out of engagement with the other's. A double-acting fluid-operated piston is formed of (a) an inner piston plate with an outer cylindrical wall portion, (b) a radially outwardly projecting member that urges the friction elements into driving contact, and (c) a hollow inner sleeve — all fixedly connected together. The piston plate has opposite faces of equal effective area. One drive member seals against the cylindrical wall portion and the hollow sleeve, defining with the piston a first fluid chamber on one side of the plate. A hollow shaft connected to that drive member extends inside the sleeve and coaxially through the piston plate, and is sealed against the sleeve. A sealing member carried by the shaft seals against the cylindrical wall portion and, with the shaft, defines a second fluid chamber on the opposite side of the plate. The piston is axially movable relative to the drive member, shaft, and sealing member. Passageways supply fluid to the chambers so that selectively varying pressure in at least one chamber moves the piston axially to actuate the clutch.

Claim 2 — Substantively the same invention as claim 1, but with two refinements in the piston geometry language: the piston plate has a hollow outer cylindrical wall portion, and the drive member is sealed against the internal surface of that cylindrical wall portion. (Claim 2 is the claim that dependent claims 3–5 build on, indicating it is the commercial/primary independent claim.)

Dependent claims

• Claim 3 (on claim 2) — The sealing member is sealed against the internal surface of the cylindrical wall portion.
• Claim 4 (on claim 2) — The fluid-supply passageways include apertures formed in the sleeve leading to the first fluid chamber (corresponding to ports 54/55).
• Claim 5 (on claim 2) — The "one drive member" is a rotatably mounted hollow shaft, and the other drive member is a rotatably mounted outer casing (i.e., the FIG. 2 arrangement: shaft 24 = output, casing 27 = input).

---

Prior art cited on the face of the patent

US 2,393,835 (Stevenson, 1946); US 2,437,430 (Lendrum, 1948); US 2,529,423 (Shou/Pacific Car & Foundry, 1950); US 2,775,331 (Peterson/GM, 1956); US 2,804,186 (Keir et al./Worthington, 1957); US 2,868,341 (Snoy/Borg-Warner, 1959); US 2,919,778 (Aschauer/Twin Disc, 1960); US 2,920,732 (Richards/Borg-Warner, 1960); US 2,922,314 (Johnson et al./Caterpillar, 1960); and foreign patent SE 144,355 (1954). The apparently "late" 1960 citations are explained by the patent's 1959 UK priority.

---

Points of uncertainty / caution

1. Filing-date discrepancy. The Google Patents metadata and the issue-date/filing-date pair (Jan. 5, 1960 → July 3, 1962) are consistent with a 1960 filing. However, the OCR'd specification line reads "Filed Jan. 5, 1969, Ser. N0. 627." I am not auto-correcting this; per the assigned rule I report it literally and flag it as almost certainly an OCR error for Jan. 5, 1960, given the 1962 grant and the 1959 UK priority. This should be verified against the original printed patent or PatentCenter.
2. Application-number rendering. Google Patents shows "US627A," i.e., application Serial No. 627 (not a modern 8-digit series code). Consistent across the record.
3. Abstract. None exists on the 1962 face of the patent; the summary above is drawn from the specification's own summary and the Google "Definitions" extraction.
4. Current assignee. "Rolls Royce PLC" is Google's attribution/entity-rename artifact; verify chain of title via USPTO Assignment if legally material.
5. Class discrepancy. Front page says Cl. 192-86; FreePatentsOnline places it at 192/85.38 and Google assigns CPC F16D25/0638. These differ in granularity and I did not reconcile them against the printed original.

I'll research whether US patent 3042167 has any litigation history.

Litigation search: US Patent 3,042,167

Bottom line: I found no record of any litigation involving US Patent 3,042,167 ("Friction clutches," Rolls-Royce Limited, filed Jan. 5, 1960, granted July 3, 1962).

What I searched

The Google Patents page for US3042167A itself contains no "Litigation" section or litigation-style entries. Its only forward citations are five patents ("Cited By"), of which three (US9413722B1, US9560176B2, US9686193B2, all Centripetal Networks) are in unrelated technology areas and are patent-to-patent citations, not litigation references.

Important caveats

1. Strict rule respected — I searched literally for 3042167 / 3,042,167. Hits such as FR3042167B1, JP3042167B2, SE144355C1-assigned Greek EDB entry 3042167 (Multibrid GmbH), and Indian trademark 3042167 are different identifiers covering different subject matter, and I am not treating them as this patent.
2. This patent expired well before modern docketing systems. Google Patents records an "anticipated expiration" of 1979-07-03 (17 years from the 1962 grant, under pre-URAA law), with the legal status "Expired – Lifetime." Any infringement suit would have had to be filed decades before PACER, CourtListener, Unified Patents, or Docket Navigator existed. Pre-1980s federal filings are frequently not digitized or indexed by these tools, and this is a likely reason for the absence of hits — not proof that none was ever filed.
3. Even if litigation once existed, it is now entirely moot. The patent has been expired for over 45 years; 35 U.S.C. § 286 limits recovery to six years before suit, so no damages claim could survive today.
4. I cannot confirm a negative with certainty. I can only state that no litigation was discoverable through the sources and queries above. A definitive answer would require a manual search of pre-1980 paper docket records (e.g., N.D. Ohio, S.D.N.Y., D. Del. indexes of the 1960s–70s) or a paid Docket Navigator/LEXIS historical search, which I cannot access here.

If you need further confirmation

• Request a full "Litigation" / "Post-Grant" tab analysis from a paid database (Docket Navigator, LexisNexis IP Litigation, Westlaw Litigation Analytics).
• Run the USPTO Patent Assignment Search for recordations of the '167 patent, which can hint at licensing/enforcement activity even where suits are not indexed.
• Search the Federal Reporter/F.2d and the Court of Claims series for "Petrie" or "Rolls-Royce" plus "friction clutch" if a historical suit is suspected.

Plaintiff(s), defendant(s), jurisdiction, case number, filing date, outcome: Not applicable — no case identified.

Proceedings overview

Total AIA trial proceedings on file against US 3,042,167: zero (0 active, 0 claims invalidated, 0 claims sustained, 0 settled, 0 institution denials) — and the bottom line for a defendant is not "the patent is hardened" but "the patent is dead": it expired 1979-07-03, 33 years before the first IPR could legally be filed, so there is no live claim to invalidate, no PTAB record to mine, and any demand letter citing this patent as an enforceable right is facially defective.

---

Why there are no proceedings to iterate — the structural answer

The instruction to source the list from the structured "PTAB proceedings on file" block is satisfied: that block reports no AIA trial proceedings for this patent as of the most recent ingest. My web searches for 3,042,167 / 3042167 returned no IPR, PGR, or CBM docket, no petition, and no PTAB or Federal Circuit decision. There is also no AIA trial could plausibly exist here, for reasons that are mechanical rather than evidentiary:

The patent's entire enforceable life ended roughly 33 years before the PTAB's IPR jurisdiction began. Note carefully that expiration is not a jurisdictional bar — the Board retains authority over expired patents, and the Federal Circuit has affirmed that repeatedly, including in Apple Inc. v. Gesture Tech. Partners, LLC, 127 F.4th 364 (Fed. Cir. 2025) (rejecting the Article III challenge to IPR of expired claims), and Sony Corp. v. Iancu, 924 F.3d 1235 (Fed. Cir. 2019). So the absence of proceedings is not a legal impossibility. It is an economic one: 35 U.S.C. § 286 caps back damages at six years before the complaint, and enforcement here would require acts of infringement occurring on or before 1979. No petitioner has ever had a reason to spend $300k–$500k on an IPR against a patent whose last possible act of infringement was during the Carter administration.

Data-quality caveats, stated plainly rather than papered over:

• The Google Patents page for this patent shows a "Cited By" list containing US 9,413,722; US 9,560,176; and US 9,686,193 (Centripetal Networks, 2013–2015 priority). Those are not PTAB proceedings against the '167 patent — they are citation-graph artifacts of Google's similarity algorithm. Do not treat them as prior challenges.
• The genuine cited-by patents (US 3,437,187 Komatsu 1969; US 4,090,597 Folomin 1978) are ordinary forward citations from the art, not validity attacks.
• The Google Patents record does not list any ex parte reexamination certificate or reissue. I did not find evidence of one, and I make no affirmative claim either way — no reexamination history is on file in the sources I checked.

---

Strategic summary

Claim status: all claims UNTESTED — and permanently so. Claims 1–5 of US 3,042,167 were never adjudicated by the Board or by any Article III court that I can locate. There is no IPR FWD to quote, no claim cancellation certificate, and no estoppel order. The claim set stands as issued, but that statement is close to meaningless: claim 1 covers a double-acting fluid-operated piston with equal effective piston faces in a multiplate friction clutch, and it lapsed into the public domain on 1979-07-03 along with the rest of the disclosure. There are no "surviving claims" to narrow around, because nothing was ever narrowed.

Estoppel landscape: not applicable, and your real exposure runs the other way. Section 315(e)(2) estoppel requires a petitioner and an instituted IPR; here there is neither, so no prior-art ground is foreclosed to you. Practically, the '167 patent is far more valuable to you as prior art and as a freedom-to-operate safe harbor than it is as a threat. Any apparatus you build that reads on its 1962 disclosure is unencumbered by it — the subject matter is public domain. The defensive work is: (1) confirm your accused product is being asserted against this patent number and not a later, live Rolls-Royce or successor patent that happens to share a family resemblance (candidate live relatives in the same technical space include US 3,088,563, "Fluid coupling and friction clutches," and US 3,053,324, both also Rolls-Royce-era filings); and (2) if you intend to use the '167 disclosure as § 102/§ 103 art against someone else's later patent, its 1959 priority date makes it excellent art — that is its residual litigation value.

Pattern signals: none exist, and none can. There is no repeat petitioner, no Unified Patents or other defensive aggregator in the chain, no Patent Owner appeal activity, no POPR, no rehearing request, no Director Review. Rolls-Royce has never appeared before the PTAB on this patent, and there is no indication of any assertion campaign. The usual heuristic — "a well-asserted patent eventually attracts IPRs" — is inapposite: the reason this patent attracted no IPRs is that it has been dead for over four decades, not that it is a hardened survivor. Treat silence here as termination of the property right, not as survivorship.

---

Recommended next steps

• If you have received a demand letter or licensing solicitation citing US 3,042,167, treat it as a strong indicator of a bad-faith or mass-mailed demand. The patent's term ended 1979-07-03 per its own Google Patents bibliographic record (https://patents.google.com/patent/US3042167/en), corroborated by the "Anticipated expiration 1979-07-03" entry in the structured data and the "Expired - Lifetime" legal status. An expired patent cannot be infringed going forward, and any pre-1979 conduct is time-barred by 35 U.S.C. § 286. Preserve the letter and consider a false-marking or unfair-competition posture rather than preparing an invalidity defense.
• If the assertion is actually against a different patent number, verify the number before responding. Confirm on the PTAB's public docket at https://ptacts.uspto.gov/ (PTAB E2E / PTACTS) and cross-check the litigation docket on CourtListener; the '167 number may be a typo, a false-marking citation, or a family reference rather than the asserted right.
• If no demand has been made — say so plainly in your file: there is no PTAB activity on US 3,042,167, and there is no live patent right to challenge. No institution deadline, no oral hearing date, and no FWD due date exist to track, because no trial was ever instituted. Filing an IPR would be a waste of budget; the correct defensive move is to confirm the patent is expired and stop there.
• For your own patenting and FTO work, the '167 disclosure is now permanently dedicated to the public and its 1959 priority date makes it citable art. That is the only remaining leverage it carries.

Caveat on live-search limits: If you need certainty beyond the ODP ingest and the searches above, the authoritative check is a PTAB E2E / PTACTS proceeding search for "3,042,167" (or application serial 627) at https://ptacts.uspto.gov/, plus a CourtListener docket search for the patent number. I found no proceeding, no petition, and no appeal in any source I could reach, and I have not invented proceeding numbers to fill the template.

I'll research the assignment record for this patent. Let me run several targeted queries.

Let me try additional searches targeting assignment databases directly.

Let me try a few more specific queries to confirm the assignment record status.

Ownership-chain reconstruction — US 3,042,167 ("Friction clutches")

Important limitation up front. I could not directly query the USPTO Patent Assignment Center from this environment, and the web searches I ran (assignment.uspto.gov + patent number; "3,042,167" + reel/frame; "Rolls-Royce" + US3042167) returned no assignment records for this patent. Independently, the Google Patents legal-events list for US3042167A contains only filing, grant, publication and anticipated-expiration events — no "Assignment" legal event of any kind. I found no reel/frame data. Everything below is therefore built from the printed patent front matter, Google Patents bibliographic data, and the sibling patents of the same inventor pair; no assignment is fabricated and none is asserted where no record exists. Treat the null result itself as the finding, subject to the pre-1980 digitization caveat noted in the Assignment timeline section.

---

Inventors

Pattern check — no adverse pattern.

• Both inventors assigned to their employer at filing ("assignors to Rolls-Royce Limited, Derby, England, a company of Great Britain"), the classic employed-inventor fact pattern in 1959–60 British practice.
• There is no evidence of inventors departing the original assignee within 12 months. On the contrary, the pair co-filed at least two further applications after this one, both assigned to Rolls-Royce Limited: US 3,088,563 ("Fluid coupling and friction clutches", filed June 22, 1960, GB priority June 25, 1959) and US 3,171,522 ("Plate clutch", filed Dec. 1, 1961, GB priority Dec. 1960). Continued co-filing with the same assignee after the priority date is the opposite of a pre-fire-sale departure pattern.
• This is an internally generated, employer-owned portfolio (a clutch family built by the same two RR engineers over 1959–61), not inventor-owned IP later peddled.

---

Original assignee

• Entity on the issued patent: Rolls-Royce Limited, Derby, England, a company of Great Britain — as printed on the patent and in the assignor clause.
• Normalization flag (not a contradiction in fact): Google Patents lists the "Original Assignee" as Rolls Royce PLC and the "Current Assignee" as Rolls Royce PLC. At the 1959 priority / 1960 filing date the legal entity was Rolls-Royce Limited, not plc (the plc form dates from the 1987 privatisation of the state-owned successor). Google Patents retro-applies the modern corporate name; the printed document's "Rolls-Royce Limited" is authoritative for the filing date. I treat these as the same corporate line, recorded under a later name.
• Primary line of business: aero-engine design and manufacture (turboprops, turbojets, gas turbines); the patent's own stated application is a turbo-prop engine installation on a rotary-wing aircraft, where the clutch couples the low-pressure turbine to an auxiliary axial-flow compressor that supplies compressed air used to generate the rotor motive fluid (see the description, and FIGURE 1).
• Did they ship a product embodying the claims? Unclear. The claimed subject matter is a wet, multi-plate, double-acting hydraulically actuated clutch with equal effective piston areas to cancel centrifugal pressure rise. The described installation is a specific rotary-wing/auxiliary-compressor architecture of the late 1950s. I found no product literature confirming a production article reading on claim 1 or claim 2; I will not assert one.
• Current status: The corporate line is operating — Rolls-Royce Holdings plc / Rolls-Royce plc, listed on the LSE. Note that Rolls-Royce Limited itself entered receivership in February 1971 as a UK insolvency, its engine business being taken over by the government-owned Rolls-Royce (1971) Limited (renamed Rolls-Royce Limited in 1977) and privatised from 1987 as Rolls-Royce plc. I found no record that this patent was conveyed in those proceedings, and a UK receivership is not a Chapter 7/11 case.

---

Assignment timeline

No assignment has been recorded for US 3,042,167 in any source I could reach.

• The only transfer disclosed on the face of the document is the original inventor→employer assignment implicit in the assignor clause ("assignors to Rolls-Royce Limited, Derby, England, a company of Great Britain"). This is the original ownership statement, not a post-issuance recorded conveyance, and no reel/frame is available for it in the online databases I searched.
• Google Patents US3042167A legal events show exactly four entries and no assignment:
  • 1960-01-05 — application filed by Rolls-Royce
  • 1962-07-03 — application granted
  • 1962-07-03 — publication of US3042167A
  • 1979-07-03 — anticipated expiration; legal status "Expired – Lifetime"
• No "Litigation" event appears either, consistent with the earlier litigation section of this analysis (no case identified).

Why the null result is expected, not surprising. USPTO's Patent Assignment Search database generally covers records recorded from 1980 onward; pre-1980 conveyances sit on microfilm reels that are only partially indexed and are frequently not keyword-searchable by patent number. Any 1960s–70s Rolls-Royce internal recording for this patent would very probably fall outside the online index. Absence of a hit is therefore weak evidence about the 1960s–70s record and strong evidence only that no modern (post-1980) assignment was recorded — which is exactly what one would expect for a patent that expired in 1979 and was never sold.

Per the task instruction, I would normally stop here once the Assignment Center is shown to hold no records. The remaining sections are supplied in the requested order, but they are thin by construction.

---

Timeline diagram

timeline
    title Ownership of US 3042167
    1959 : GB priority application filed Feb 23
    1960 : US application filed Jan 5
    1962 : Patent granted Jul 3
         : Inventors assigned to Rolls-Royce Limited
    1971 : Rolls-Royce Limited enters receivership
    1979 : Anticipated expiration Jul 3
    1987 : Successor renamed Rolls-Royce plc

(No event above is a recorded USPTO patent assignment except the original inventor-to-employer statement; the 1971 and 1987 entries are corporate-history context for the current assignee name and are not evidence of a recorded conveyance of this patent.)

---

NPE / troll-pattern signals

Corroborating negative: the sibling patents by the same two inventors (US 3,088,563 and US 3,171,522) also show Rolls Royce PLC as current assignee — i.e., the whole clutch family stayed with the operating company. A single patent migrating to an asserter while its siblings did not would be a red flag; that did not happen here.

---

Verdict

Insufficient data — no assignment records found beyond the original inventor-to-employer ownership statement.

The patent issued to Rolls-Royce Limited (printed front matter; Google Patents shows the normalized successor name Rolls Royce PLC) and there is no recorded post-issuance assignment, no reel/frame, and no correspondent of record in any source I could reach; Google Patents' sole legal events are the 1960-01-05 filing, the 1962-07-03 grant/publication, and the 1979-07-03 anticipated expiration. All eight NPE signals are not present, and the sibling patents by the same inventor pair remained with Rolls-Royce. The most likely reality — subject to the pre-1980 microfilm indexing gap, which I cannot close from here — is that the patent simply expired in the original assignee's hands and was never traded.

Verify at: USPTO Assignment Center and the legacy Patent Assignment Search — search patent number 3042167; a definitive check of the 1960s–70s record would require a manual reel search at the USPTO Public Search Facility, which I cannot perform here.

I'll research the prior-art citations for US 3,042,167, verifying each reference on USPTO and other authoritative sources.

Let me verify the remaining cited references.

Prior-Art Analysis — US 3,042,167 ("Friction Clutches")

Note on scope and sourcing. Per your strict rule, I treated the identifier 3042167 literally throughout and did not fold in hits for FR3042167B1, JP3042167B2, Greek EDB 3042167 (Multibrid GmbH), Indian trademark 3042167, or any other similar string. The authoritative text supplied for this task (the Google Patents full text of US3042167A) is the primary source; I verified the three closest references against their own USPTO/Google Patents records via web search. Where I could not verify a reference's content in this session, I say so explicitly rather than characterizing it from memory.

Step-budget caveat: I was able to verify US2868341, US2920732 and US2919778 in detail, and confirm the bibliographic record of US2393835. My searches for US2437430, US2529423, US2775331, US2804186 and US2922314 were cut off by the tool step limit, so for those five I rely on the patent's own "References Cited" list (which supplies number, inventor, date and title) and flag descriptions as unverified.

---

1. USPTO record for the patent under analysis

Source: https://patents.google.com/patent/US3042167/en

Because the application was filed in 1960, pre-AIA 35 U.S.C. §§ 102/103 governs. For the §102 analysis below, the controlling critical date is the February 23, 1959 UK priority date (with §102(e) available as of each reference's U.S. filing date).

---

2. The patent's own cited prior art (10 references)

Google Patents lists nine U.S. patents and one Swedish patent as "Patent Citations" for US3042167A. Full citation, dates, and what each reference was doing:

All nine U.S. patents pre-date the invention under §§ 102(a)/(b)/(e) — references 7, 8 and 9 are §102(e) art by virtue of their 1955–56 filing dates (they granted in Jan. 1960, on or about the '167 filing date, so their grant dates alone would not qualify them, but their filing dates do). SE 144,355 (1954) is a §102(a)/(b) foreign printed publication.

Forward-citation noise to disregard. The "Cited By" list on US3042167A contains US9413722B1, US9560176B2 and US9686193B2 — all Centripetal Networks network-security patents. These are unrelated-art patent-to-patent citations, not prior art and not litigation references; they have no bearing on §102 here. (This corroborates the litigation summary already produced — no litigation is disclosed.)

---

3. Element-by-element mapping to the claims

To assess anticipation, here is the element set of the independent claims:

Claim 1 elements: (a) input + output drive members; (b) friction elements on each, movable into/out of engagement; (c) double-acting fluid-operated piston comprising an inner piston plate with an outer cylindrical wall portion, a radially outwardly projecting member urging the friction elements into contact, and a hollow inner sleeve, all fixedly connected; (d) piston plate opposite faces of equal effective area; (e) one drive member sealed against the cylindrical wall portion and the hollow sleeve, defining a first fluid chamber; (f) a hollow shaft connected to that drive member, extending inwardly of the sleeve and coaxially through the piston plate, sealed against the sleeve; (g) a sealing member carried by the shaft, sealed against the cylindrical wall, defining a second fluid chamber on the opposite side; (h) piston axially movable relative to the drive member, shaft and sealing member; (i) fluid passageways.

Claim 2 repeats (a)–(i) but recites the piston plate as having a hollow outer cylindrical wall portion, with the drive member sealed against its internal surface and the sleeve defining the first chamber. Claim 3 adds that the sealing member seals against the internal surface of the cylindrical wall. Claim 4 adds apertures in the sleeve leading to the first fluid chamber. Claim 5 specifies the drive members (rotatable hollow shaft as one, rotatable outer casing as the other).

---

4. Per-reference §102 assessment

A. Strongest candidates (double-acting, hydraulically balanced clutch piston)

US 2,868,341 A — Snoy, "Double acting clutch," Borg-Warner Corp.
Filed 1957-04-01 (Ser. No. 649,830); granted 1959-01-13. Verified via USPTO/Google Patents full text.
Disclosure: A double-acting hydraulic clutch in which an annular reaction plate 8, sealed (ring 13) against the bore of an imperforate piston housing 14, divides the housing interior into two spaced fluid chambers 15 and 16; annular pistons 17 and 47 are axially movable on shaft 1 with seals (18, 48) running against the internal surface of the piston housing; the pistons carry circumferentially spaced apertures (21, 51) providing metered cooling flow of fluid to the clutch plates; one-way flap valves 41 in openings 37 of the reaction plate control transfer between the two sides; the specification expressly notes hydraulic balance and rapid action. It is the parent of the Richards/Snoy copending application Ser. No. 593,479 (i.e. reference 9).
Sources: https://patents.google.com/patent/US2868341 ; https://patentimages.storage.googleapis.com/22/9e/3d/2c5bab8099716f/US2868341.pdf
§102 relevance: Best single-reference challenge to the "double-acting piston with opposed chambers separated by a plate and seals running on a cylindrical wall" concept, and directly pertinent to claim 4-type metered-flow apertures, and to the fluid-supply/passageway element (i). It does not disclose the "hollow inner sleeve / hollow shaft coaxially through the piston plate" architecture or the "equal effective area" limitation in the specific form claimed. → Anticipates, at most, a sub-combination; not claim 1 or 2 as a whole. A §103 combination with reference 9 is the more realistic threat.

US 2,920,732 A — Richards & Snoy, "Double hydraulic operated clutch device," Borg-Warner Corp.
Filed 1956-06-25 (Ser. No. 593,479); granted 1960-01-12; 18 claims, Cl. 192-87. Verified.
Disclosure: Opposed clutch packs on a rotating shaft, actuated by a piston disposed between them; shaft bore 2 with tube 3 forming annular channel 4 and radial ports 5/6 for separate low/high-pressure feeds; reaction plate 8 sealed to piston housing 14 and dividing it into chambers 15/16; explicit stated object: "in which the effects of centrifugal force on the hydraulic fluid in the rotating clutch are nullified"; another object: housing maintained filled with hydraulic fluid at all times, clutch actuation by raising pressure in one portion; apertures 21/51 provide metered cooling flow to the clutch plates.
Source: https://patents.google.com/patent/[US2920732A](/patent/US2920732A)/en
§102 relevance: This is the single most on-point reference for the rotating-fluid-centrifugal-balance problem that the '167 patent's own specification identifies as the invention's raison d'être ("Since, however, the opposite faces of the piston 38 are of substantially the same effective area, the effect of centrifugal force is balanced across the piston"). It discloses the coaxial hollow-shaft-plus-inner-tube dual-pressure feed arrangement (element (f)-adjacent). It does not disclose the claimed piston made up of a plate + skirt + hollow sleeve fixed together, nor equal effective areas across a single piston plate. → Strong §102(e)/§103 reference against the balance concept; not a complete anticipator of claims 1–2.

US 2,919,778 A — Aschauer, "Hydraulically operated, multiple clutch," Twin Disc Clutch Co.
Filed 1955-08-11 (Ser. No. 527,706); granted 1960-01-05; 9 claims, Cl. 192-86. Verified.
Disclosure: Concentric, radially nested inner and outer hydraulically actuated clutches; two clutch-engaging pistons 26 and 35 tied together by radial connector 39; the specification states the "connected concentric and clutch engaging pistons responsive to the actuating medium and area conditioned to insure complete hydraulic balance at all speeds and axial positions of the pistons", and expressly addresses the centrifugal-force problem and the axial-force equation, noting that the areas are deliberately dissimilar to nullify centrifugal effects. Dual pressure supplies via pipes 43/49, passages 44–57, and control valve 61.
Source: https://patents.google.com/patent/[US2919778A](/patent/US2919778A)/en
§102 relevance: Anticipates the general principle of hydraulically balancing a rotating clutch's actuating pistons against centrifugal force, i.e. the "balanced across the piston" feature that the '167 preamble/description treats as inventive. Critically, Aschauer achieves balance with unequal areas, which cuts against (and is useful to distinguish) the '167 claim 1/2 requirement that the opposite faces be of equal effective area. → §102/§103 reference to the result, not to the claimed means.

B. Secondary / background references (verified bibliographically, content not fully re-verified this session)

US 2,393,835 A — Stevenson, "Control for friction clutches," Stevenson Engineering Corp. Filed 1942-03-30, granted 1946-01-29. Bibliographic record confirmed (patenthub CPC listings; Google Patents citation in WO1991002900A1). A control reference for friction clutches — relevant only to actuation/control context, not to piston architecture. → No §102 anticipation of claims 1–5.

US 2,437,430 A — Lawrence, "Hydraulic clutch control." Filed 1945-10-29, granted 1948-03-09. Hydraulic actuation/control art. → Background; no anticipation.

US 2,529,423 A — Shou, "Transmission mechanism," Pacific Car & Foundry Co. Filed 1948-01-14, granted 1950-11-07. Transmission environment; possibly relevant to plural-clutch engagement sequencing. → Background; no anticipation.

US 2,775,331 A — Peterson, "Clutch with coolant metering," General Motors Corp. Filed 1951-06-02, granted 1956-12-25. Directly relevant to the "wetting of the clutch plates … to ensure an appropriate coefficient of friction" feature of the '167 specification and to claim 4-style metering apertures. → Relevant to the lubrication sub-feature; no complete anticipation.

US 2,804,186 A — Keir et al., "Clutch safety mechanism," Worthington Corp. Filed 1955-04-20, granted 1957-08-27. Safety/fail-safe actuation. → Background; no anticipation.

US 2,922,314 A — Johnson et al., "Automatic planetary transmission and control therefor," Caterpillar Tractor Co. Filed 1955-03-01, granted 1960-01-26. Transmission control context (cf. the Snoy selector-valve art cited in later Borg-Warner patents). → Background; no anticipation.

SE 144,355 C1 (1954-03-02). Foreign art of record; content not retrieved. Treated strictly as a foreign printed publication under §102(a)/(b). → Cannot assess without the document.

---

5. Bottom line

1. No single one of the ten cited references anticipates claims 1 or 2 as a whole. Claims 1–2 are a specific structural combination (piston plate + radially projecting urging member + hollow inner sleeve fixed together; hollow shaft coaxially through the plate; sealing member carried by the shaft separating two chambers; seals running on the cylindrical wall). None of the references, as far as I can verify, discloses that particular geometry inside an input-casing/output-shaft wet clutch.
2. The most relevant prior art is, in order:

• US 2,920,732 A (Richards & Snoy) and US 2,868,341 A (Snoy) — both Borg-Warner, both double-acting, two-chamber, hydraulically-balanced, oil-metered clutches; Richards & Snoy even states the centrifugal-nullification object verbatim in substance. These are the principal §102(e)/§103 threats, and are the references a challenger would lead with.
• US 2,919,778 A (Aschauer) — the "hydraulic balance against centrifugal force at all speeds" concept, but with deliberately unequal areas, which distinguishes it from the "equal effective area" requirement of claim 1/2.
• US 2,775,331 A (Peterson) — coolant/lubricant metering to the clutch plates (relevant to claim 4-style apertures and to the plate-wetting feature).

1. The genuinely distinguishing feature of the '167 claims over the Borg-Warner/Twin Disc art is the specific equal-effective-area, single-piston-plate construction with the concentric hollow-sleeve/hollow-shaft sealing arrangement, achieving centrifugal balance by area equality rather than by the unequal-area (Aschauer) or reaction-plate/one-way-valve (Richards & Snoy, Snoy) approaches. Expect any §103 attack to combine US 2,920,732 with US 2,868,341, and to argue that equalizing the areas was an obvious design choice.
2. Caveats I want on the record:

• I could not retrieve full text for US 2,437,430, US 2,529,423, US 2,775,331, US 2,804,186, US 2,922,314 or SE 144,355 within this session's step budget. Their characterizations above are limited to title/date/assignee from the patent's own citation list plus general field context — I am not asserting specific disclosure content for them.
• Anticipation under §102 requires a single reference disclosing every element arranged as claimed. On the record I have, the cited art supports obviousness combinations under §103 far more strongly than outright anticipation.
• This is a technical prior-art mapping, not a legal validity opinion.

I'll pull the actual disclosures of the cited references before mapping them to the claims, since titles alone won't support a §103 analysis.

Good — these confirm the key references. Let me pull the remaining cited references to complete the mapping.

Obviousness Analysis — US 3,042,167 under 35 U.S.C. § 103

Building on the previously generated bibliographic, claim, and litigation sections. That work established the claim set, the cited-art list, and the 1959/1960 dates, so I won't restate them. One housekeeping note: the session header gives today as 2026‑09‑29 while this task specifies April 26, 2026. The discrepancy is immaterial here — this is a 1962 patent expired since 1979 — but I flag it per the no-auto-correction rule.

---

1. Evidentiary posture (read this before relying on any mapping below)

Verified from primary text during this analysis:

Not verified — treated as unexamined: US 2,393,835 (Stevenson), US 2,437,430 (Lendrum), US 2,529,423 (Shou), US 2,804,186 (Keir et al.), US 2,922,314 (Johnson et al.), SE 144,355. My retrieval budget ran out before I could read their specifications. I am not asserting what they disclose. Their titles suggest control, safety, and transmission subject matter rather than rotating-actuator piston geometry, so the § 103 case below deliberately does not depend on them; they would be cited, if at all, only as cumulative evidence that hydraulic friction-clutch actuation was a crowded art by 1955–57.

Also unknown: the page does not distinguish examiner-cited from applicant-cited art, nor identify which reference(s) formed the actual ground of rejection. So I cannot say what the examiner relied on in 1960–61. The analysis below is a fresh, de novo § 103 assessment.

---

2. Governing law and critical date

• Priority: 23 February 1959 (GB). US filing: 5 January 1960. Grant: 3 July 1962.
• Pre‑AIA law governs (1952 Act, as amended). § 103 was in force from 1 January 1953.
• Every verified reference was filed before 23 February 1959, so all qualify as § 102(e) prior art and are combinable:
  • '778 filed 11 Aug 1955 • '732 filed 25 Jun 1956 • '341 filed 1 Apr 1957 • '331 filed 2 Jun 1951 (also § 102(b) as of 25 Dec 1956). SE 144,355 published 2 Mar 1954 → § 102(b) printed publication.
• § 103(c) common-ownership disqualification is irrelevant (different assignees: GM, Borg‑Warner, Twin Disc) and postdates this patent.
• Standard of review: Graham v. John Deere factors, applied with KSR's flexibility. I note explicitly that KSR (2007) is retrospective as to this 1960 filing; I use the modern rationales because they now govern any re-litigation of validity, but I identify where a 1961 examiner would have had a harder articulation problem.

PHOSITA: a mechanical design engineer with ~3–5 years in hydraulically actuated friction clutches for gas-turbine and heavy-vehicle transmissions, familiar with (i) interleaved wet multi-plate packs and splined thrust-plate clamping, (ii) piston/cylinder actuation and its sealing, (iii) centrifugal effects on actuating oil in rotating chambers, (iv) coaxial fluid feed through hollow rotating shafts (concentric tubes, drilled shafts), and (v) mean-plus-function claim interpretation under § 112 ¶ 6.

---

3. Claim 1 decomposed into limitations

Claim 2 narrows L3 (cylindrical wall portion is hollow) and L5 (sealing against the internal surface). Claims 3–5 add: sealing member sealed to the internal surface (C3); apertures in the sleeve leading to the first chamber (C4); hollow-shaft-vs-outer-casing drive-member identity (C5).

Prosecution note: L9 is a means‑plus‑function clause under § 112 ¶ 6. Its scope is the disclosed structures (concentric tubes 51/52, annular clearance 53, ports 54/55/73/76, drillings 45, lines 71/74, muffs 72/75, valve 68) and equivalents. That materially broadens L9 for § 103 purposes — any two-concentric-path rotary feed plus a selector valve is an equivalent. By contrast, C4's "apertures in said sleeve" is structural and narrow.

---

4. Verified disclosure findings, mapped to the limitations

US 2,775,331 (Peterson / GM) — the closest structural reference

https://patents.google.com/patent/US2775331 • https://patentimages.storage.googleapis.com/3e/08/9a/8abab5cbf9c94f/US2775331.pdf

Verified text establishes: a clutch "primarily intended for use in coupling a gas turbine power unit to an air‑[compressor]" [OCR truncated]; driving drum 16 with external splines 17; driven drum 12 splined to shaft 11; interleaved driven plates 18 and driving plates 19; "The plates are pressed together by an annular cylinder 20 movable axially with respect to the shaft 10"; "The cylinder 20 slides on a sleeve 23 fixed on the shaft 10, the sleeve 23 being integral with a web 24 which constitutes an annular piston. This piston divides the cylinder 20 into two chambers 26 and 27."; actuating oil fed "through concentric tubes 28 and 29 disposed on the axis of the clutch, radial passages in a fitting 31 pressed into the shaft, and radial passages through the shaft 10 and sleeve 23 into the chambers 26 and 27"; chamber 27 has a bleed 32 and a centrifugal bleed valve 33 "to release some of the fluid from the disengaging chamber 27 so that the centrifugal effect of fluid in this chamber tending to release the clutch is reduced"; coolant oil routed via tube 34, chamber 36, and drum passages 37 to wet the clutch plates.

Maps to: L1, L2, L3(a)+(b) (web 24 = piston plate; cylinder 20 = the outwardly projecting thrust member), L5 (partial — chambers 26/27 aboard a single rotary assembly), L6 (partial — coaxial sleeve 23 on hollow shaft 10; concentric tubes 28/29 in the shaft axis), L7 (partial — web 24 divides the two chambers), L8 (cylinder/member axially movable relative to the shaft), L9 (tubes 28/29 + fitting 31 + external valve = § 112 ¶ 6 equivalents), plus wet-plate cooling (spec-only, not claimed).

Does not disclose L4. '331 recognizes the centrifugal problem in a rotating clutch but solves it by venting (bleed 32 / valve 33), not by equalizing effective areas.

Critical structural observation: because web 24 is an annular piston reciprocating inside annular cylinder 20, its two faces are bounded by the same cylinder bore and the same sleeve OD — i.e., they are geometrically equal-area as a matter of construction. '331 therefore appears to inherently present equal-area piston faces, while being entirely silent on why that matters. I flag this as a possible anticipation question under § 102(b), not merely obviousness — but I cannot confirm it without '331's full drawing sheet and claims, which I did not retrieve.

US 2,912,778 / US 2,919,778 (Aschauer / Twin Disc) — the "equal-area balance" teaching

https://patents.google.com/patent/[US2919778A](/patent/US2919778A)/en

Verified text: objects include a dual hydraulically actuated clutch with "connected concentric and clutch engaging pistons responsive to the actuating medium and area conditioned to insure complete hydraulic balance at all speeds and axial positions of the pistons." The specification states: "A particular advantage of the foregoing construction is the hydraulic balancing of the connected pistons 26 and 35 in any axial position by the opposing thrusts of the oil fills in the cylinders. This arrangement has special value in high speed clutches since there is no tendency for either piston to shift from neutral to engaged position due to centrifugal force acting on the oil in the associated cylinder. To achieve this result … the area of the inner piston 35 that is exposed to the oil fill is substantially larger than the like area of the outer piston 26. This relationship is determined by ascertaining the force acting axially due to centrifugal force according to the following, experimentally derived equation…" followed by F = K W N²[R₀⁴ − 2R_B²(R₀²+R₁²) − R₁⁴].

Also verified: cylinders 19 and 34 are "maintained in a filled condition to compensate for leakage and promote quicker engaging action," even in neutral, under a small pressure (~5 psi), with the pressure selectively raised by a control valve 61 to engage either clutch — i.e., permanently-pressurized chambers with selective pressure increase, which is structurally the same control philosophy as '167's permanently-low-pressure chamber 56 plus selectively-high-pressure chamber 60.

Maps to: L4 (the teaching), L2/L3 (interleaved multi-plate packs; connected concentric clutch-engaging pistons tied by radial connector 39), L5/L6 (annular cylinder 34 between wall 33 and annulus 30; input flange 10 / hub 11; coaxial output sleeve 37 journaled on bearing 38), L9 (passages 44–57, pump 58, valve 61).

Key caveat for the applicant: '778 achieves balance with unequal areas. That is the single best nonobviousness lever, and I address it in § 7.

US 2,868,341 (Snoy / Borg‑Warner) — the sealing topology and coaxial feed

https://patents.google.com/patent/US2868341

Verified: rotating shaft 1 with axial bore 2; imperforate tube 3 inside the bore defining annular fluid channel 4; radial ports 5 (to channel 4) and 6 (to tube 3) through the shaft; reaction plate 8 "disposed upon the shaft 1 for rotation therewith" and "prevented from axial movement by snap rings 9," having an outer groove 12 with sealing ring 13 "disposed in engagement with the inner surface of a generally annular piston housing 14 which is imperforate so as to contain hydraulic fluid," the plate "in effect divid[ing] the interior of piston housing 14 into a pair of spaced fluid chambers 15 and 16"; annular piston 17 "mounted to the shaft 1 so as to be axially movable with respect thereto," its outer periphery carrying seal 18 engaged with the inner surface of housing 14; apertures 21 "through an inner portion of piston 17 to provide metered cooling flow of fluid to the clutch plates"; sealing means 22 between the shaft and the piston's annular central opening; snap rings 19/24 arresting piston travel; and the stated object of operating "with a lower hydraulic pressure than heretofore possible while yet retaining features of hydraulic balance."

There is also a second piston 47 with seal 48 against the same housing inner surface, and one‑way valve arrangements in openings 37 of the reaction plate, explicitly described in the sibling '732 as "control[ling] transfer of hydraulic fluid from one compartment adjacent one side of the reaction plate to the compartment at the opposite side."

Maps to: L7 (reaction plate 8 = a sealing member carried by the rotating shaft, sealed against the cylindrical wall's internal surface), L5-as-narrowed-by-claim-2 (sealing against the internal surface of the cylindrical wall portion), L6 (hollow shaft with two coaxial fluid paths), L8, L9 (ports 5, 6 + external valving), C3 (directly), C4-adjacent (apertures through a piston component to a chamber/plate).

US 2,920,732 (Richards & Snoy / Borg‑Warner) — the express centrifugal-nullification object

Verified: "Another object of the present invention is to provide a hydraulically operated clutch mechanism … in which the effects of centrifugal force on the hydraulic fluid in the rotating clutch are nullified." Further: "a piston housing … maintained filled with hydraulic fluid at all times, clutch actuation being effected by increasing the fluid pressure in one portion of the housing"; "the piston housing is axially movable with either of the two pistons disposed therein"; the housing is "divided into two portions by a reaction plate"; ledge 27 has "a plurality of spaced openings 32 … to effect fluid communication between the port 6 and the chamber 15"; a snap ring 30 normally positions piston 28.

This reference is important on three independent limitation groups: L4's entire rationale, L9/control scheme, and L8 (which member is the movable one).

---

5. Combination 1 (primary): Peterson '331 + Aschauer '778

Coverage. '331 alone carries L1, L2, L3(a)–(b), L8, L9, and most of L5–L7, and is in the identical field — a hydraulically actuated multi-plate clutch coupling a gas-turbine power unit to a driven shaft, with oil deliberately routed to wet the plates. '778 supplies the one missing element, L4, and supplies it as a stated design principle ("area conditioned to insure complete hydraulic balance at all speeds and axial positions"), complete with an experimentally derived formula for setting the areas.

Motivation to combine — this is not a hindsight paste-up, because '331 states the problem itself. '331 discloses a centrifugal bleed valve 33 whose only stated purpose is "to release some of the fluid from the disengaging chamber 27 so that the centrifugal effect of fluid in this chamber tending to release the clutch is reduced." A PHOSITA reading '331 in 1959 is therefore handed both the problem (centrifugal pressure in a rotating actuating chamber tends to release the clutch) and a remedial step (vent the disengaging chamber), with '331's own language conceding the remedial step is only a reduction, not an elimination. '778 sits in the same class as the patent itself ('167's front page reads "Claims. (Cl. 192‑86)"; '778 reads "9 Claims. (Cl. 192‑86)"), addresses rotating high-speed clutches, and offers the intellectually cleaner fix: rather than bleeding oil and losing actuating force, condition the exposed areas so the centrifugal thrusts cancel. Substituting a known, superior remedy for a known, acknowledged-partial remedy in the same device is the paradigm KSR rationale of "use of a known technique to improve a similar device in the same way," and it is also a simple substitution of one known element for another yielding a predictable result.

Reasonable expectation of success is documented, not assumed. '778 supplies the governing equation and states that the balance holds "in any axial position" — i.e., it is not an empirical guess but a calculable design condition. That squarely rebuts any "obvious to try, but no predictable result" argument.

Where the combination is short. '331's movable member is the cylinder, with the sleeve 23 and piston web 24 fixed to the shaft; '167 requires the piston plate, thrust member, and hollow inner sleeve to be fixedly connected together and the assembly to be the movable part (L3, L8). Combination 1 therefore still needs a rationale for that redistribution, which Combination 2 supplies.

---

6. Combination 2: Peterson '331 + Snoy '341 + Richards '732 + Aschauer '778

This four-reference set closes every limitation, including the awkward L3/L8 "which member moves" issue and C3/C4.

Step 1 — Topology (add '341). '341 supplies the L5/L6/L7/C3 sealing and feed architecture almost verbatim: an imperforate rotating housing with an internal surface; a plate carried by and rotating with the shaft and sealed at its periphery against that internal surface by seal 13; the plate dividing the interior into two chambers; an annular piston axially movable on the shaft with a peripheral seal against the same internal surface; and a hollow shaft carrying two coaxial fluid paths (bore 2 / tube 3 / annulus 4 / ports 5 and 6). '341 is assigned to the same company as '732 and is expressly an improvement on '732.

Step 2 — Which member moves (add '732). '732 states in terms: "the piston housing is axially movable with either of the two pistons disposed therein." Meanwhile '341 presents a piston movable on the shaft, and '331 presents a cylinder movable on the shaft. The art therefore expressly and repeatedly recognizes that in this exact family of devices either the outer wall member or the inner/shaft-mounted member may be the movable one, that choice being driven by which part must carry the thrust plate. Given that express teaching, moving the hollow inner sleeve from the fixed side ('331) to the movable assembly ('167) — while preserving the same seal interface between sleeve and shaft — is a rearrangement of parts with no new result, the classic obviousness rationale for mere inversion of parts.

Step 3 — The anti-centrifugal design rule (add '778, motivated by '732 and '341). '732's first-listed object is to "nullify" centrifugal effects in the rotating clutch; '341's object is to operate "with a lower hydraulic pressure than heretofore possible while yet retaining features of hydraulic balance." '778 supplies the area-conditioning rule plus the equation. Three independent references in the same art articulate the same objective, and one of them supplies the calculable means. That is a textbook KSR rational (a): known elements combined according to known methods, with predictable results.

Step 4 — The control scheme (add '732 and '778). '167's claim 1 requires that "on selectively varying of fluid pressure in at least one of said fluid chambers, the piston is moved axially so as to actuate the clutch." '732 discloses a housing "maintained filled with hydraulic fluid at all times, clutch actuation being effected by increasing the fluid pressure in one portion of the housing." '778 discloses cylinders held filled even in neutral at ~5 psi with a control valve 61 raising pressure to engage. That is '167's low-pressure-always-on chamber 56 / high-pressure-on-demand chamber 60 scheme, in substance and in function. Under § 112 ¶ 6, L9's "means" is satisfied by '732's ports 5/6 or '341's ports 5/6 or '331's concentric tubes 28/29 — all equivalents of the disclosed tubes 51/52 and valve 68.

Claim 4 specifically. "Apertures in said sleeve … leading to said first fluid chamber" finds counterparts in '732's openings 32 through ledge 27 communicating port 6 with chamber 15, and in '331's radial passages through sleeve 23 into chambers 26/27. C4 adds essentially nothing over the combination.

Claim 5 specifically. Hollow-shaft-one-member / outer-casing-the-other is the ordinary architecture of this entire art (drum 16 splined externally, driven drum 12 splined to shaft 11 in '331; input flange 10 with hub 11 and coaxial output sleeve 37 in '778; casing/shaft in '341). C5 is a structural recital of the conventional arrangement and would not independently patent.

Claim 3 specifically. "Sealing member … sealed against the internal surface of said cylindrical wall portion" is, on my reading, '341's seal 13 on reaction plate 8 engaging the inner surface of piston housing 14. On the verified text, C3 may be anticipated by '341 rather than merely obvious over it.

---

7. The best nonobviousness arguments, and how they fare

Argument 1 — '778 teaches away by requiring unequal areas. Strongest point available. '778 states "the area of the inner piston 35 … is substantially larger than the like area of the outer piston 26," and derives a formula in which the two areas are deliberately asymmetric. Rebuttal: the asymmetry in '778 arises because its two pistons sit at different radii and in different cylinders, so equal areas there would not balance. The '167 piston is a single plate whose two faces sit at the same radial station in a common chamber pair, where equal areas is the limiting case that makes the centrifugal integrals cancel trivially. '167's own specification says exactly this ("Since … the opposite faces of the piston 38 are of substantially the same effective area, the effect of centrifugal force is balanced"). A reference does not teach away merely because it solves a differently-geometried version of the problem by different means; and '778's stated objective — no tendency to shift due to centrifugal force — is identical to '167's. Expect an examiner to win this point, but it is a genuine, arguable distinction worth preserving.

Argument 2 — No reference discloses the three-part rigid piston assembly (plate + thrust skirt + hollow inner sleeve) with the hollow shaft passing coaxially through the plate and sealed to the sleeve. Genuine gap on the verified record. '331 divides the assembly differently (web + sleeve fixed; cylinder movable). '341 mounts its piston directly on the shaft without an interposed sleeve. Rebuttal under § 103: the difference is where the sleeve sits, not whether one exists — '331 has a hollow sleeve coaxial with and sealed to the shaft ('167 L6's interface, in kind); '732 expressly authorizes putting the housing/movable wall on either side; and no new or unexpected function is asserted for the relocation. This is the limitation on which the patent most plausibly issued and the one on which a validity challenge would most likely founder in 1961 — but it is a relocation argument, not a results argument, and KSR discounts such arguments absent unexpected results.

Argument 3 — "Filed Jan. 5, 1969" in the OCR'd specification line. Already flagged in the earlier section as an OCR error for 1960. It does not affect the § 103 critical date (priority 23 Feb 1959) but should be resolved against the printed original if the filing date is ever load-bearing.

Argument 4 (not available on this record) — secondary considerations. The '167 specification advertises exactly the advantages that '732 and '778 already promised: lower actuation pressure ('341 also promises this), balanced/centrifugal-independent operation ('732, '778), and wet-plate friction control ('331's tube 34/passages 37, '341's apertures 21). Because the asserted advantages were known desiderata of the art, the patent faces an In re Geisler/KSR "expected result" problem rather than an unexpected-results shield. Any rebuttal would need proof of commercial success of the claimed clutch (e.g., the Rolls‑Royce Tyne/turbo-prop rotor-drive application described in the spec) with a demonstrated nexus to L4 specifically — and, critically, success attributable to the equal-area balancing, not to the gas-turbine/rotor system as a whole. No such evidence appears in the record I have.

---

8. Claim-by-claim conclusion

Overall: the patent's surviving inventive contribution over the verified prior art is narrow and, in my assessment, does not rise to a § 103 patentable difference. The single non‑trivial distinction is the rigid three‑part piston assembly with the hollow sleeve on the movable side, and the specification itself supplies the admission that motivates the equal-area feature ("if the faces … were of different effective area, the effect of centrifugal force could be to alter the differential … to such an extent that the piston 38 would be moved so as to effect disengagement"). That is an express acknowledgment of a known problem, which strengthens rather than weakens the case for obviousness.

---

9. Residual uncertainties and what would change the answer

1. I did not read '331's full specification or drawings. If '331's cylinder 20 is stepped (as '341's piston 47 and '732's piston 28 are, with ledges and snap-ring stop faces), its piston faces may not be equal-area, which would remove both the anticipation hypothesis and part of the Combination 1 story. This is the highest-value item to verify.
2. I did not read US 2,804,186 (Keir/Worthington), US 2,922,314 (Johnson/Caterpillar), US 2,529,423 (Shou), US 2,437,430 (Lendrum), US 2,393,835 (Stevenson), or SE 144,355. Any of these could disclose the three-part rigid piston assembly, which would harden the obviousness case considerably. Their titles suggest otherwise, but I am not asserting their contents.
3. I cannot identify the actual grounds of rejection or what the examiner considered closest art; the Google Patents citation list encodes no examiner/third-party distinction for the "Citations" block.
4. Anticipation vs. obviousness for claim 1 turns on the US2775331 figures, which I could not retrieve.
5. The "Definitions" extraction on the Google page (restating the double-acting, equal-effective-area summary) is drawn from the specification, and the page's prior-art keywords are piston, shaft, clutch, sleeve, fluid — consistent with, but not evidence of, the art mapping above.
6. Ignore the Centripetal Networks "Cited By" entries (US 9,413,722; 9,560,176; 9,686,193) — as flagged in the earlier section, these are unrelated network-security patents and cast no light on § 103 here.

Bottom line: on the verified record, claims 1, 2, 4 and 5 are obvious under § 103 over Peterson '331 in view of Aschauer '778, with Snoy '341 and Richards/Snoy '732 supplying the sealing topology, the movable-member design choice, and the permanently-pressurized/selectively-boosted control scheme; claim 3 is most likely anticipated by '341. The analysis is contingent on the two verification gaps in items 1 and 2 above.