US 6751537

I'll search for authoritative information on US patent 6751537, including any recent litigation or docket activity.

Let me verify litigation/docket status specifically for this patent and confirm the assignee history.

Verification & Scope Note

I searched for US patent 6751537 specifically. Two important clarifications before the summary:

1. A similarly-numbered but unrelated patent exists. Japanese patent JP 6751537 B2 (特許第6751537号, issued 2020‑09‑09) is a completely different document owned by 株式会社A.L.I. Technologies, titled "ハイブリッド有人飛行体" (hybrid manned aircraft). It is not the same patent family and must not be conflated with US 6,751,537. Every hit for the bare string "6751537" in my searches resolved to this Japanese aircraft patent, the US damper patent, or unrelated matters.

2. No CAFC 2026 docket activity found. I found no Federal Circuit appeal, PTAB proceeding, or 2026 district-court docket involving US 6,751,537. Searches surfaced unrelated 2026 CAFC cases (e.g., US Patent No. 7,679,637 LLC v. Google LLC, No. 2024‑1520, decided Jan. 22, 2026 — a web-conferencing §101 case) and unrelated Mando litigation (e.g., a 2025 Hanyang/Mahauto dispute concerning ADAS steering-angle technology; Jaguar Land Rover v. Mando, No. 2‑16‑cv‑11545 (E.D. Mich.), settled Jan. 2017 — both unrelated to this patent). I cannot confirm any 2026 litigation activity; treat that as an absence of evidence, not evidence of absence, since I cannot exhaustively query PACER/CAFC dockets with these tools.

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Bibliographic Data — US 6,751,537 B2

Assignee note: the Google Patents assignment record names the inventor as "KOH, YOU‑SEOK" (reel 012437/0615). A separate, later assignment entry in a citing document renders the name "KOU, YOUSEOK" (reel 014415/0831). I am reporting these literally; the discrepancy is likely a transliteration variant, but I have not verified which is authoritative. "HL Mando Corp" is the rebranded successor to Mando Corporation.

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Abstract (as issued)

A method for controlling a vehicle damper having front and rear dampers, where damping force is controlled by data from a steering angle sensor, a vehicle speed sensor, and a yaw rate sensor. Steps: (a) input steering angle, vehicle speed, and yaw rate data; (b) calculate a desired yaw rate using the steering angle data, vehicle speed data, and a vehicle specification; (c) compare the desired yaw rate with the measured yaw rate; (d) determine whether the vehicle is over‑steered or under‑steered based on the comparison; and (e) control the damping force in response to that determination.

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Plain-Language Overview of the Independent Claims

Claim 1 — Basic over‑steer/under‑steer damping control

A method of controlling a vehicle's front and rear dampers, where a steering angle sensor, a vehicle speed sensor, and a yaw rate sensor supply the control inputs. The method:

• (a) reads steering angle, vehicle speed, and yaw rate;
• (b) computes a desired yaw rate from the steering angle, vehicle speed, and a vehicle specification (e.g., wheelbase);
• (c) compares that desired yaw rate against the measured yaw rate;
• (d) characterizes the vehicle as over‑steered or under‑steered from that comparison; and
• (e) sets the damper damping force based on that characterization.

Essentially: compute what the car "should" be yawing at for the given steering and speed, see whether the actual yaw is more or less than that, and use the resulting over/under‑steer classification to tune the dampers. The specific formula and the specific front-vs-rear force direction are left to the dependent claims.

Claim 4 — Over/under‑steer control plus road-slipperiness detection

Broader sensor set and an added decision step. The vehicle has front and rear dampers; inputs come from a steering angle sensor, yaw rate sensor, lateral G sensor, wheel speed sensor, and vehicle speed sensor. The method:

• (a) reads steering angle, yaw rate, lateral G, wheel speed, and vehicle speed data;
• (b) computes a desired yaw rate from steering angle and vehicle speed;
• (c) compares desired vs. measured yaw rate;
• (d) classifies the vehicle as over‑steered or under‑steered;
• (e) additionally decides whether the road surface is slippery, using the vehicle speed data, the lateral G data, and a vehicle specification; and
• (f) controls damping force in response to both determinations from (d) and (e).

Essentially: same over/under‑steer logic as Claim 1, but with more sensors feeding the controller and a second, independent judgment about whether the road itself is low‑friction (low‑myu) — damping is then set from the combination of the two.

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Dependent Claims (7 total) — brief map

• 2 (dep. 1): Defines the classification inequality — if δ·(φ̇d − φ̇ms) ≥ 0 → under‑steered; if ≤ 0 → over‑steered, where φ̇d = desired yaw rate, φ̇ms = measured yaw rate, δ = steering angle.
• 3 (dep. 1): Defines the force direction — over‑steer: decrease rear, increase front; under‑steer: increase rear, decrease front.
• 5 (dep. 4): Same inequality as claim 2, applied in the claim‑4 context.
• 6 (dep. 4): Slipperiness is judged by comparing the difference between the measured lateral G and a calculated lateral G (derived from vehicle speed and the vehicle specification) against a predetermined value.
• 7 (dep. claim 3): States that if over‑steer is found and the road is in a low‑myu condition, rear damping is decreased and front increased; if under‑steer is found with low myu, the reverse.

Literal-reading caveat (no auto-correction applied): Claim 7 is written as depending from claim 3, yet it recites steps "(e)" and "(f)" — steps that exist only in independent claim 4. Read literally, claim 7's dependency and its step references are inconsistent. This is a drafting irregularity in the issued patent; I am reporting it as written rather than "fixing" it. Similarly, claims 2 and 5 shorthand the term list as "{dot over (φ)}d . {dot over (φ)}ms and δ" (period rather than comma), which reads as a punctuation artifact.

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Technical/Prosecution Context

• The specification frames the invention against conventional control logics tuned for high‑myu (high friction) roads that "cannot cope with a spin phenomenon" on low‑myu surfaces (ice/snow) and "may not effectively deal with an over‑steer or an under‑steer" during abrupt steering. The stated object is improved steering stability by adjusting front/rear damping based on steering status.
• The stated control premise (spec., describing step 38/50): "the more a damping force decreases, the more a grounding force increases during a steering operation," and the method "can be applied regardless of whether the vehicle turns in a left direction or in a right direction" — i.e., the control is symmetric and sign‑agnostic apart from the δ product term.
• Two embodiments are disclosed: FIG. 2 (first embodiment → claim 1 family: steering angle, yaw rate, vehicle speed) and FIG. 3 (second embodiment → claim 4 family: adds lateral G and wheel speed sensors and the slipperiness determination).

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Confidence & Limits

• High confidence on title, application/filing/issue/priority dates, inventor, claims text, and family members — all corroborated by the Google Patents full text, Espacenet claims view, and FreePatentsOnline.
• Moderate confidence on the "current assignee = HL Mando Corp" label — it is Google Patents' automated reassignment listing; no recorded assignment document changing ownership from Mando Corporation to HL Mando appears in the record I retrieved (the only recorded assignments concern the initial inventor→Mando transfer). The HL Mando name likely reflects corporate renaming rather than a recorded conveyance, but I cannot confirm that from the retrieved documents.
• Low/negative confidence on any CAFC 2026 docket: no such activity was found, and given the patent lapsed in 2016 for non‑payment of maintenance fees, 2026 appellate activity is unlikely (though a lapsed patent could theoretically still be the subject of an appeal over pre‑lapse conduct — I found no such record).
• I could not directly query PACER, the CAFC docket system, or USPTO PatentCenter with these tools; those sources should be consulted for an authoritative litigation-history confirmation.

I'll research litigation involving US patent 6751537 across litigation databases and court records.

Let me search litigation-specific databases for this patent.

Let me check dedicated litigation databases and the patent's litigation docket directly.

Litigation Search Results: US Patent No. 6,751,537

Bottom line: I found no record of any litigation, PTAB proceeding, or ITC investigation involving US Patent No. 6,751,537.

What the searches covered

I ran multiple targeted queries across patent-litigation and general web sources, including queries phrased as:

• "US6751537 patent litigation"
• "6751537" patent lawsuit
• "6751537" OR "6,751,537" district court complaint infringement
• "6,751,537" patent asserted defendants
• Unified Patents / docket-style queries for the number
• Mando Corporation + damper + 6751537

None of these returned a district court docket, a CAFC appeal, a PTAB (IPR/PGR/CBM) filing, or an ITC Section 337 investigation naming this patent.³

Patent identity confirmation (to avoid a wrong-number match)

Before concluding, I confirmed the patent under search matches the identifier literally:

Important number-match caution: the searches also surfaced unrelated items bearing the same digits, which I excluded because they are not the US patent:

• JP 6751537 B2 — a Japanese patent (特許第6751537号, granted 2020-09-09) for a "ハイブリッド有人飛行体" (hybrid manned aircraft / aerial vehicle) by A.L.I. Technologies. This is a different patent in a different jurisdiction, not US 6,751,537.
• A Lithuanian company-registry notice number 6751537 (UAB Mateikų įmonė filing). Not a patent.

One related matter worth flagging (but NOT this patent)

There is a well-publicized Bosch v. Mando patent dispute: Robert Bosch filed suit against Mando Corporation in the U.S. (reported ~September 2016), and Mando counterclaimed that Bosch infringed two Mando patents (an electronic brake control system and a solenoid valve for a brake system).¹ That case involved brake/ESC/ABS patents — not the '537 damper-control patent. It is a Mando litigation, but it does not involve US 6,751,537, so it should not be listed as litigation over this patent. Notably, Mando's asserted patents in that action were brake-related, not the suspension/damper patent at issue here.

Assessment / caveats

• The absence of results is consistent with the patent's status: the '537 patent lapsed in 2016 for failure to pay maintenance fees, so it has been unenforceable for roughly a decade and would be an unlikely candidate for a shell/NPE assertion campaign that would generate searchable litigation records.
• Confidence level: Moderate-to-high that no litigation exists. I could not directly query PACER, the CAFC docket, or the Unified Patents litigation caselist within the available search steps, so I cannot rule out a sealed or very obscure filing. If a definitive negative is required for a legal opinion, I recommend a direct confirmatory check on:
  • Unified Patents litigation portal: https://portal.unifiedpatents.com/litigation/caselist
  • PACER / CourtListener docket search for "6,751,537" and "6751537"
  • USPTO Patent Center / PTAB for any IPR/PGR against the '537 patent
  • CAFC docket search

Litigation list

No known litigation involving US Patent No. 6,751,537.

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¹ Korea Times, "Mando pressed to pay for patent infringement," 2017-01-13 (Bosch–Mando U.S. dispute; patents at issue were brake/ESC-related, not US 6,751,537).
³ Sources consulted included Google Patents family/citation data for US6751537 and general litigation-oriented web searches. Patent-forward citations listed for US6751537 (e.g., US 6,556,909; later Honda and Mando patents) are patent-to-patent citations, not litigation references.

Proceedings overview

Total AIA trial proceedings on file for US 6,751,537: ZERO. The USPTO Open Data Portal structured block returned no IPR, PGR, or CBM for this patent as of the most recent ingest, and my independent web searches surfaced no AIA petition, institution decision, Final Written Decision, or Federal Circuit appeal naming U.S. Patent No. 6,751,537 (breakdown by status is therefore 0 active / 0 claims invalidated / 0 claims sustained / 0 settled / 0 institution denied). The bottom-line defensive posture is not "hardened patent that survived IPRs" and not "claims canceled in an IPR" — it is something better for a defendant: the patent lapsed for failure to pay maintenance fees effective 2016-06-15 and is recorded as "Expired – Fee Related," so the claims are untested at the PTAB and, more importantly, no longer enforceable. A demand letter citing US 6,751,537 today is asserting a dead patent.

Because there are no proceedings, the per-proceeding template below has no entries. I have not fabricated proceeding numbers, panels, or dispositions to fill the space.

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Proceedings on file

None. No IPR20xx-#####, PGR20xx-#####, or CBM20xx-##### proceeding is associated with U.S. Patent No. 6,751,537 in the structured PTAB data or in any public source I could locate.

Corroborating evidence

• Canonical source (USPTO ODP via prompt): "no AIA trial proceedings for this patent as of the most recent ingest."
• Google Patents record for US6751537B2 (https://patents.google.com/patent/US6751537/en): the "Cited By" and "Families Citing this family" tables list only patent documents (e.g., US20040038599A1 / US7083172B2 to Mando; US7885740B2 to Honda; US11618440B2 to Guangzhou Automobile; Polaris documents). There is no PTAB "Cited By"/proceeding block, and the only citation of this patent is US 6,556,909 B2 (Nissan, lane-keep control) — a patent citation, not an AIA trial.
• Legal Events for US6751537B2 (same page), verbatim: 2016-01-22 REMI Maintenance fee reminder mailed; 2016-06-15 LAPS Lapse for failure to pay maintenance fees; 2016-07-08 / 2016-07-11 STCH Information on status: patent discontinuation — PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362; 2016-08-02 FP Lapsed due to failure to pay maintenance fee — Effective date: 20160615. Header status: Expired - Fee Related , expires 2022-07-29 (the 2022-07-29 figure is the PTA-adjusted nominal term; it is superseded as a practical matter by the 2016-06-15 lapse).

Do not be misled by number collisions

My searches repeatedly returned different patents with superficially similar numbers. None of these is US 6,751,537, and none is a proceeding on it:

Anyone (or any AI tool) conflating these with your patent number is making a factual error. Verify by patent number and title ("Method for controlling a damper of a vehicle"), not by trailing digits.

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Strategic summary

Claim status of US 6,751,537: UNTESTED at the PTAB, and now unenforceable. All seven issued claims — independent claims 1 and 4, and dependent claims 2, 3, 5, 6, and 7 — were never subjected to an AIA trial. Claims 1–3 are directed to the basic steering-angle/vehicle-speed/yaw-rate damper-control method, including the over-steer/under-steer decision on the sign of δ·({dot over (φ)}_d − {dot over (φ)}_ms) (claim 2) and the front-hard/rear-soft vs. front-soft/rear-hard damping split (claim 3); claims 4–6 add the lateral-G and wheel-speed inputs and the slippery-road determination; claim 7 (which depends from claim 3) recites the low-myu variant. Nothing was canceled, nothing was confirmed, nothing was amended. The more consequential development is administrative, not adversarial: the maintenance-fee lapse effective 2016-06-15 terminated the patent's enforceability. The priority date is 2001-09-12 (KR 10-2001-0056092), the U.S. filing date is 2001-12-28 (App. No. 10/033,870), and the patent issued 2004-06-15.

Estoppel landscape — § 315(e)(2) is a non-issue here. Because no IPR/PGR reached a final written decision, no petitioner (or privy) is estopped under 35 U.S.C. § 315(e)(2) / § 325(e)(2), and there is no IPR record to borrow for a § 315(b) time-bar argument against a late-filed petition by a co-defendant. Conversely, a defendant gains nothing from IPR estoppel — but it also doesn't need it. The far stronger defenses are non-enforceability of the lapsed patent and the damages bar: under 35 U.S.C. § 286, a patentee cannot recover damages for infringement occurring more than six years before the complaint is filed. With the patent dead as of 2016-06-15, a complaint filed in 2026 reaches back only to 2020 — a period during which the patent was already expired and no infringement was actionable. Practically, that should zero out recoverable damages (verify against the specific docket and any pre-lapse notice letters).

Pattern signals — none that matter. No petitioner filed once, let alone multiple times; there is no defensive aggregator (no Unified Patents, RPX, or similar) in the chain; the patent owner (Mando Corporation, now HL Mando Corp) never had to defend an AIA trial and therefore never pursued a PTAB appeal. U.S. Patent No. 6,751,537 was evidently never a high-value assertion vehicle — it issued in 2004 into the ECS damper-control space, its family member EP1304241B1 expired for non-payment of fees (per the Google Patents country-status table), and the whole family's commercial relevance faded with the 2000s-era electronically controlled suspension generation it describes. There is no litigation-driven IPR history attached to this number.

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Recommended next steps

• Do not file an IPR. With no PTAB activity and a patent that lapsed on 2016-06-15, an AIA petition would spend six figures to invalidate a patent that is already unenforceable. There is no defensive benefit.
• Lead with the lapse. Pull the USPTO Patent Center maintenance-fee record (https://patentcenter.uspto.gov) for US 6,751,537 and confirm the 37 CFR 1.362 lapse event of 2016-06-15. That single fact, plus the § 286 six-year damages limit, is the whole defense.
• If a demand letter or complaint is actually served, check two things: (1) the assertion date versus the 2016-06-15 lapse, and (2) whether any pre-lapse notice letter or covenant could support a claim for the 2010–2016 window (already outside § 286 for a 2026 filing). If the letter cites claims 1–7, note that none of those claims has ever been adjudicated by the PTAB — the patentee cannot point to any FWD preserving them, and there is no litigation record I could find either.
• Plainly state the absence. If you are drafting an invalidity/unenforceability opinion, say it directly: no AIA trial proceeding has ever been filed against U.S. Patent No. 6,751,537, and the patent expired for failure to pay maintenance fees effective 2016-06-15.
• Caveat on completeness. I could not access the ODP API directly; the "no proceedings" conclusion rests on the structured PTAB block supplied in this prompt plus public-search corroboration. A belt-and-suspenders check is a direct search of PTAB E2E (https://ptacts.uspto.gov/ptacts/) and the PTAB Decisions page (https://www.uspto.gov/patents/patent-trial-and-appeal-board/ptab-decisions) by patent number — I found nothing, and I would expect nothing, but I flag it rather than overstate certainty.

I'll research the assignment record for US 6751537, starting with the recorded assignment data in the patent record and cross-referencing USPTO Assignment Center and supporting sources.

Let me drill into the Assignment Center record, the correspondent of record, and the Mando → HL Mando corporate history.

Let me search for the specific assignment reel/frame and any change-of-name filings.

Inventors

Pattern notes: There is only one inventor, which is normal for a narrow application-level control-logic patent of this type. The assignment was executed 2001-12-24 — four days before the 2001-12-28 US filing and just over three months after the 2001-09-12 KR priority — i.e., a routine pre-filing inventor-to-employer assignment, not a post-filing cleanup. No unusual departure or inventor-holdout pattern is detectable from the record. I did not find any evidence of inventors leaving Mando around the filing window; the "all inventors depart within 12 months" fire-sale precursor is not present on the data available. (Caveat: I could not query Korean employment/HR records, so this is a negative finding on the patent record only, not a positive confirmation of continuous employment.)

Original assignee

Mando Corporation — the entity named on the issued patent and the named "applicant" on the published application. Mando is a Korea-based, publicly listed (KOSPI: 204320) Tier-1 automotive supplier, not a holding or licensing vehicle. Its business is split into a Mobility Dynamic System segment (brakes, ABS/TCS/ESC, steering/EPS) and a Ride Comfort System segment that specifically produces electronically controlled suspensions (ECS) and continuous damping controls (CDCs) — the exact product class this patent (front/rear damper damping-force control) reads on. So yes, the original assignee shipped products embodying the claims — damper/CDC control is a core Mando product line, and Mando has publicly won large suspension contracts (e.g., reported Volkswagen suspension-unit award). Current status: operating. The company did not dissolve or go bankrupt; instead it renamed itself to HL Mando Corporation (에이치엘만도 주식회사), resolved at a special shareholders' meeting on 2022-09-05, under the HL (formerly Halla) Group. Corporate-history note: Mando had been split in 2014 into a holding company (Halla/HL Holdings) and an operating Mando, so the operating entity persisted across the rename.

⚠️ Flag / contradiction to note: Google Patents lists the "Current Assignee" as HL Mando Corp, but no change-of-name assignment for Mando → HL Mando appears in the patent's recorded legal events. That field appears to be Google's assignee-name normalization (same corporate family carried forward under the new name), not evidence of a recorded USPTO assignment. Treat "HL Mando Corp is the recorded owner" as unverified; the last recorded owner of record is Mando Corporation.

Assignment timeline

Exactly one assignment is recorded against this patent. The chain is one link long.

• 2001-12-24 (executed) / recorded 2001-12-28 — Reel 012437 / 0615
  • Conveyance: Assignment (Assignment of Assignors Interest)
  • Assignor: KOH, You-Seok (sole inventor)
  • Assignee: MANDO CORPORATION (Korea, Republic of)
  • Correspondent: Not recoverable from the sources retrieved. The Google Patents legal-events entry for the '537 patent records the reel/frame, owner name, assignor, and effective date, but does not expose the correspondent of record. I could not retrieve the Assignment Center entry itself within the available search steps, so I will not guess at the attorney/firm. (This is the single most important field left open — see Verdict caveat.)
  • Context: Routine pre-filing inventor-to-employer assignment. Standard for an employee-engineer invention at a Korean supplier; not an acquisition, fire-sale, reorg, securitization, or transfer-to-asserter.

Post-issuance fee/maintenance actions (not assignments):

• 2007-11-16 — maintenance fee paid (4th year)
• 2011-09-20 — maintenance fee paid (8th year)
• 2016-01-22 — maintenance-fee reminder mailed; 2016-06-15 — lapsed for failure to pay maintenance fees (patent expired due to non-payment under 37 CFR 1.362). No assignment accompanied the lapse.

No later recorded assignment exists — no transfer to any LLC, no security agreement, no merger, no license recordation, no defensive-aggregator acquisition. The patent remained with Mando Corporation through expiration.

Timeline diagram

timeline
    title Ownership of US 6751537
    2001 : Inventor assignment to Mando recorded
         : Reel 012437 frame 0615 executed 2001 Dec 24
    2004 : Patent issued June 15
    2016 : Lapsed for unpaid maintenance fees
    2022 : Owner renamed HL Mando per corporate resolution
         : No change of name recorded on this patent

NPE / troll-pattern signals

Verdict

Insufficient data (only the original assignment is recorded).

This is the literal fit: the USPTO-recorded chain consists of one link — inventor You-Seok Koh → Mando Corporation, Reel 012437/0615, executed 2001-12-24 and recorded 2001-12-28 — followed only by fee events and the 2016-06-15 lapse for non-payment of maintenance fees. Every NPE signal is absent: there is no shell-entity transfer, no known asserter, no cascading LLC chain, no bankruptcy sale, and no defensive-aggregator terminus, because there is simply no post-issuance assignment of any kind. The owner of record is (and has throughout been) an operating Tier-1 auto-parts manufacturer whose product line includes the CDC/ECS damper controls this patent covers, so the chain has the hallmarks of ordinary in-house corporate ownership, not an assertion vehicle. Caveat for a definitive opinion: I could not open the Assignment Center detail screen to capture (a) the correspondent of record for Reel 012437/0615 and (b) whether any Mando → HL Mando change-of-name record exists that is not reflected in the patent's Google-Patents legal events; both should be confirmed directly at the USPTO Assignment Center by searching patent number 6,751,537.

Verification links:

• USPTO Assignment Center (search by patent number): https://assignmentcenter.uspto.gov/ — also indexed at https://assignment.uspto.gov/patent/index.html
• Google Patents legal events for US6751537 (source of the Reel 012437/0615 entry): https://patents.google.com/patent/[US6751537B2](/patent/US6751537B2)/en

I'll verify the patent record and research each cited reference before building the § 102 analysis.

I have strong detail on the examiner-cited reference and the family-cited Toyota art. Let me verify a few more of the family-cited references.

Prior-Art Analysis for US 6,751,537 B2

0. Record verification (patent number literal match)

Before analyzing the art, I confirmed the identifier resolves to the correct US document and not to any similar number:

⚠️ Number-collision warning (carried forward): the string "6751537" also resolves to JP 6751537 B2 (A.L.I. Technologies, hybrid manned aircraft) — a different patent, different jurisdiction. It is excluded here. Everything below concerns US 6,751,537 B2.

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1. Statutory framework and critical dates

Because US 6,751,537 has an effective filing date of 2001‑12‑28, the pre‑AIA 35 U.S.C. § 102 governs. Anticipation under § 102 requires that a single reference disclose every element of the claim, arranged as claimed. The controlling dates are:

• § 102(b) statutory bar — publication/patenting more than one year before filing → before 2000‑12‑28.
• § 102(a) — patented/published/known before the invention (measured from the 2001‑09‑12 priority).
• § 102(e) — a U.S. patent/grant, effective as prior art as of its own U.S. filing date.

I also note from the record that the patent issued with only one examiner-cited reference, which is itself evidence that the examiner did not find a § 102 single-reference anticipation of the independent claims.

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2. The citation record — two distinct categories

The '537 record contains two different sets of references, which must not be conflated:

1. Examiner-cited art on the face of the U.S. patent — exactly one item ("Patent Citations (1)"): US 6,556,909 B2.
2. "Family Cites Families" (17 items) — references cited in the prosecution of the family siblings (EP 1304241, JP 2003‑080914, KR 100709011, DE 60127412), i.e., art considered against the same disclosure in other jurisdictions, but not listed on the U.S. face. These are nonetheless legitimate § 102 prior-art candidates for the shared disclosure and are analyzed below.

⚠️ Provenance caveat: category‑2 items were retrieved from the family-citation record, not the U.S. front page. Their § 102 effect depends on publication date (below), not on where they were cited.

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3. Examiner-cited reference (U.S. face)

Assessment: Given the pre‑AIA single-reference rule, US 6,556,909 cannot anticipate independent claim 1 (missing the "controlling the damping force of the damper in response to an over/under‑steer determination" element) or claim 4 (missing the damping-force and slipperiness elements). It is best characterized as cited for general context, consistent with its listing as the sole citation.

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4. Family-cited references (17) — citation, dates, description, § 102 status

Dates are given as (priority / publication). § 102 category is assessed against the 2000‑12‑28 bar and 2001‑09‑12 priority.

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5. Substantive § 102 analysis of the most relevant references

The independent claims have two essential, conjunctive thrusts: (i) an over/under‑steer classification derived from a desired‑yaw‑rate‑vs‑measured‑yaw‑rate comparison (claims 1(c)–(d), 4(c)–(d); inequality in claims 2, 5) and (ii) control of the damper damping force responsive to that classification (claims 1(e), 3, 4(f), 7). The dependent‑claim slipperiness feature (claims 4(e), 6) is a third distinct element. I analyze each reference against these three prongs.

(a) US 4,761,022 A (Toyota) — the closest reference on the classification logic

This is the single most on‑point item in the record for the over/under‑steer detection prong:

• Discloses the same sensor set: steering‑angle sensor, vehicle‑speed sensor, yaw‑rate sensor, and lateral‑acceleration sensor (col. describing M2; see claims 4 and 6 of that patent).
• Discloses computing a "target yaw rate … calculated from the sensed steering angle and the sensed vehicle speed" and comparing sensed yaw rate vs. target yaw rate.
• Discloses using the product "the sensed yaw rate × an error of the sensed yaw rate from a target yaw rate" as a criterion value — functionally parallel to the '537 claim‑2 quantity δ·(φ̇d − φ̇ms).
• Discloses changing the front/rear allotment ratio so the vehicle shifts toward oversteer (when yaw lags) or understeer (on steering reversal).

§ 102 outcome: US 4,761,022 strongly discloses steps (a)–(d) of claims 1 and 4 (including the sensor set and the yaw‑rate comparison). It does not, however, disclose "controlling the damping force of the damper." Its actuator is a hydraulic actuator controlling load shift/roll‑stiffness distribution, not damper damping force. Under the strict single‑reference rule it therefore does not anticipate claims 1–7, but it is the leading § 103 candidate and is the most damaging art for the classification prong.

(b) DE 4123235 C2 (Daimler‑Benz / Zomotor et al.) — the closest reference on the inequality itself

• Claim 1 literally recites: desired yaw rate formed from vehicle speed + steering‑wheel angle; actual yaw rate from a sensor; difference = desired − actual; output signal indicating "understeer or oversteer."
• Its classification variable MULT = (μ_des − μ_act) × sign(μ_act), with MULT > 0 → understeer and MULT < 0 → oversteer. This is mathematically equivalent in sign to the '537 claim‑2 inequality δ·(φ̇d − φ̇ms) ≥ 0 → understeer; ≤ 0 → oversteer, since the steering‑angle sign δ and the sign of measured yaw rate share the same sign during a turn.
• The controlled variable is brake slip of individual wheels (front‑outside cornering wheel for oversteer; rear‑inside wheel for understeer), i.e., the same directional logic as claim 3 but executed on brakes rather than dampers.

§ 102 outcome: DE 4123235 is a strong § 102(b) reference for the classification sub‑step recited in claims 2 and 5 (and the (c)–(d) steps of claims 1/4). It does not anticipate the independent claims because it controls brakes, not damper damping force.

(c) US 5,931,887 A (GM / Hac) — reference‑model desired yaw rate

• Computes desired yaw rate from driver steering angle and vehicle speed via a transfer‑function reference model, and forms a yaw‑rate error against measured/estimated yaw rate to develop a yaw‑moment command.
• Actuator = individual wheel brakes.

§ 102 outcome: Anticipates, at most, the "calculate a desired yaw rate using steering angle and vehicle speed" step of claims 1(b)/4(b) and the comparison step. It cannot anticipate the independent claims (brake actuator ≠ damper; no slipperiness prong). Relevant § 102(b) art for the calculation step only.

(d) DE 4436162 C1 (Siemens) — driving‑stability regulation

A vehicle‑stability (yaw‑control) reference using a desired vs. actual yaw behavior with a stability‑regulation actuator (brake/engine — not a suspension damper). § 102(b) art for the reference‑model/comparison concept; cannot anticipate the damper‑force element.

(e) JPH 03‑258650 A (Toyota) — road‑surface friction‑coefficient detection

Directly relevant to the slipperiness prong of claim 4(e)/claim 6 (road‑surface µ detection). § 102(b) art. It is unlikely to anticipate claim 4 as a whole (claim 4 requires the combined over/under‑steer determination and damper control), but it is squarely relevant to the claim 6 limitation ("deciding whether the road surface is slippery" from vehicle parameters). Full text not retrieved — my assessment here is provisional.

(f) Suspension/damper references — US 4,650,212; JPH 07‑41783; DE 4010277; JPH 05‑221213; JP 3131049; JPH 07‑89315; JP 3608445; KR 10‑0226635; KR 1999‑0057521; KR 2000‑0027739

These are suspension/damping‑control references. They are relevant to the "damper" element prong of the claims (i.e., that damping is controllable), and several are road‑condition‑ or adaptive‑damping systems. Based on title/abstract‑level information I cannot assert that any of them discloses the yaw‑rate‑comparison‑based over/under‑steer classification feeding a front/rear damper‑force command, which is the point of novelty. ⚠️ Full texts not retrieved for these items — treat their § 102 potential as unassessed rather than negative. JP 3608445 B2 additionally has the publication‑date problem flagged in § 4(17).

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6. Claim‑by‑claim anticipation snapshot

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7. Bottom line and confidence

• No reference in the '537 record anticipates the independent claims 1 or 4 as a whole. The defining combination — front/rear damper‑force control commanded by a desired‑vs‑measured yaw‑rate over/under‑steer classification (and, for claim 4, a road‑slipperiness decision) — is not disclosed by any single cited item. Every close reference either (a) classifies over/under‑steer but actuates brakes or roll‑stiffness/load shift rather than damper force (US 4,761,022; DE 4123235; US 5,931,887; DE 4436162), or (b) controls dampers/suspension without the yaw‑rate classification (the suspension references).
• The strongest § 102 arguments are against the dependent limitations, not the independent claims: DE 4123235 (and to a lesser degree US 4,761,022) disclose the classification inequality of claims 2/5 almost verbatim-equivalent, and JPH 03‑258650 is on‑point for the slipperiness subject matter of claims 4(e)/6 — but each is a partial match only.
• This is consistent with the prosecution outcome (a single examiner citation; grant on the first action of record).

Confidence: High for the citation inventory, dates, and § 102 categories (taken from the authoritative patent/family record). Moderate for the element‑level disclosures of US 4,761,022, DE 4123235, US 5,931,887, US 6,556,909 (I retrieved substantive text/claims). Low/provisional for the foreign‑language suspension references (DE 4010277, JPH 07‑41783, JPH 05‑221213, JP 3131049, JPH 07‑89315, JP 3608445) and the Korean ECS references, for which I could not retrieve full texts within the available search steps — their § 102 potential is unassessed, not negated.

Recommended verification steps for a legal opinion: (1) pull the full text (and English translations) of DE 4123235 C2, US 4,761,022, JPH 03‑258650 A, and DE 4436162 C1 to confirm the element‑level disclosures; (2) confirm whether JP 3608445 had an earlier JP A‑publication that pre‑dates the 2001‑09‑12 priority; (3) confirm the U.S. front‑page citation list against USPTO Patent Center (my searches relied on Google Patents/Espacenet/FreePatentsOnline/uspto.report, not a live Patent Center query).

I'll ground this obviousness analysis in the actual prior-art references. Let me pull the key references from the patent's citation record.

Strong material. Let me ground the claim‑4/claim‑6 road‑slipperiness limitations and a few more family‑cited references.

Obviousness Analysis — US 6,751,537 B2 under 35 U.S.C. § 103

Scope note (building on prior sections): This analysis uses the prior art appearing in the patent's own citation record on its Google Patents page (https://patents.google.com/patent/US6751537/en) — i.e., the single US "References Cited" entry (US 6,556,909 B2) and the "Family Cites Families" list (17 documents). I flag explicitly which references I verified by retrieving text and which I did not. I do not fabricate disclosures for documents I could not retrieve. The claim-construction caveats already flagged (claim 7 depending from claim 3 while reciting steps "(e)"/"(f)"; overlapping "≧0" and "≦0" branches in claims 2/5) carry forward and are material to how any § 103 challenge would be run.

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1. Governing law and prior-art status

The application was filed 2001-12-28 with a KR priority of 2001-09-12, so pre-AIA § 102/§ 103 applies. Every reference discussed below predates the priority date by years and is therefore § 102(b) art, except US 6,556,909 B2, which was granted 2003-04-29 on an application whose U.S. filing predates the '537 priority date (its JP priority is 2000-04-25) and is therefore available at minimum as § 102(e) art — it was in fact the examiner's sole citation, so its availability is established by its citation.

Enabling/field requirement: all references are in vehicle dynamics / suspension control (B60G, B62D, B60T) and are reasonably pertinent to the problem of steering-condition-responsive suspension control.

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2. Person having ordinary skill in the art (POSITA)

A POSITA here would be an engineer with a bachelor's degree in mechanical, electrical, or automotive engineering and roughly 2–5 years of experience in chassis control, specifically familiarity with (i) semi-active/continuously variable damper control, (ii) yaw-rate-based vehicle stability control (the ABS/ASR/VSC "ESP" art that matured through the 1990s), and (iii) standard vehicle sensors (wheel speed, steering angle, yaw rate, lateral accelerometer). Any of the references below would have been within that person's ordinary technical grasp.

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3. Prior art inventory (with verification status)

Important provenance point: the US case had only one cited reference (US 6,556,909). US 4,650,212, US 4,761,022, and DE 4123235 appear in the family citation lists (i.e., they were before the EP/KR examiners of EP 1304241 / KR 100709011). They were therefore not of record in the US prosecution and would be the natural basis for a § 103 reexamination or invalidity contention.

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4. Element-by-element mapping — claim 1

Every element of claim 1 is disclosed or suggested across US 4,761,022 + US 4,650,212.

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5. The § 103 grounds

Ground 1 — Claim 1 obvious over US 4,761,022 in view of US 4,650,212

• US 4,761,022 supplies the entire detection chain (a)–(d): steering angle + vehicle speed + yaw rate sensors, desired yaw rate computed from steering angle, vehicle speed and vehicle characteristics, comparison with measured yaw rate, and generation of a steering-characteristic/understeer correction. Its control output, however, is a front/rear load-shift allotment via suspension actuators, not a damping force command.
• US 4,650,212 supplies the missing actuator and the front/rear distribution concept: variable damping-rate dampers at both the front and rear axles, controlled by a steering-angle/vehicle-speed controller, expressly to "give the vehicle an understeer tendency" (front hard / rear soft) or otherwise set the steering characteristic.
• Motivation to combine: both references confront the same problem — the vehicle's under-steer/over-ster balance during steering/cornering — and both use the same informational inputs (steering angle, vehicle speed). US 4,650,212 already teaches that the front/rear damping distribution maps onto the steering characteristic; US 4,761,022 already teaches the yaw-rate-error determination of what the steering characteristic should be. A POSITA seeking to close the loop needed only to feed the known yaw-rate-error signal into the known front/rear damper controller. This is the paradigm KSR combination of two known elements in a known arrangement, each performing its known function, with a predictable result (an automatically corrected steering characteristic).

Ground 2 — Claim 2 obvious

Claim 2's limitation is the sign-normalized yaw-rate error: δ·(φ̇d − φ̇ms) ≥ 0 → understeer; ≤ 0 → oversteer.

• US 4,761,022 discloses the criterion value as the product of the sensed yaw rate and the yaw-rate error (γ · error) — structurally the same signed product used to detect the direction of the turning condition.
• DE 4123235 / US 5,341,297 goes further: claim 8 computes MULT = (μ_soll − μ_ist) × sign(μ_act), where "MULT greater than zero" means understeering and "MULT less than zero" means oversteering.

Claim 2 is therefore the sign-multiplication technique, already known, with the steering angle δ substituted for the yaw rate as the sign carrier. Because sign(δ) = sign(φ̇ms) in any steady-state or near-steady cornering situation — the very situations this algorithm governs — the substitution is a design choice between equivalent, art-recognized sign carriers (KSR "interchangeability of known elements"), and δ was already a sensed input in both US 4,650,212 and US 4,761,022. Expect a strong § 103 rejection on claim 2.

(Note the drafting defect flagged earlier: because the branches are "≥ 0" and "≤ 0," the value zero falls into both branches. That is a § 112(b) problem, not a saving distinction.)

Ground 3 — Claim 3 obvious

Claim 3 sets the corrective direction: over-steer → rear damping ↓ / front ↑; under-steer → rear ↑ / front ↓.

• US 4,650,212 establishes the correlation between front/rear damping distribution and steering characteristic (front hard/rear soft → understeer tendency; the reverse → oversteer tendency). The '537's claim 3 is simply that correlation read in the corrective direction — and the specification's own stated premise ("the more a damping force decreases, the more the grounding force increases") is the mechanism a POSITA would supply, a mechanism US 4,650,212's own discussion of gripping force supports.
• DE 4123235 teaches the same axle-selection logic for a different stability actuator: on oversteer, act at the front (increase brake slip at the front outer wheel); on understeer, act at the rear (increase brake slip at the rear inner wheel). Substituting a known stability actuator (the semi-active damper) into a known stability control law, where both are known to influence yaw behaviour, is an obvious substitution of one known element for another to obtain a predictable result.
• US 4,555,126 independently confirms that the prior art adjusted the front/rear suspension-rate ratio on detection of steering to change the vehicle between oversteer and understeer.

Ground 4 — Claim 4 obvious

Claim 4 adds three things to claim 1: two more sensors (lateral G and wheel speed), and a step (e) slipperiness decision from vehicle speed + lateral G + a vehicle specification.

• Wheel-speed sensors were ubiquitous and standard in ABS/VDC systems — US 5,332,300 describes the anti-lock braking environment in which these signals are already available.
• Lateral (radial) acceleration sensor: DE 4123235's background expressly identifies "an acceleration sensor which measures the radial acceleration of the vehicle" as an alternative to a gyroscope for obtaining the actual yaw-rate value.
• Low-μ determination feeding the yaw-rate-based logic: US 5,332,300 states that stability control requires "information on the friction coefficient of the road and the vehicle speed," that μ "can be computed from the highest possible vehicle deceleration," and that the desired yaw speed can be calculated from the steering angle, the vehicle speed and the coefficient of friction. This is an express teaching, in the same field, to determine road friction and combine it with the yaw-rate-based control — exactly claim 4's step (e)/(f) architecture. The family-cited JPH 03-258650 ("Road surface frictional coefficient detecting device, Toyota) is a title-level corroboration, though I did not retrieve its text.

Ground 5 — Claim 5 obvious

Claim 5 is claim 2's inequality in the claim 4 setting — for the reasons in Ground 2.

Ground 6 — Claim 6 — the principal weakness in the § 103 case

Claim 6 defines the slipperiness test as comparing the difference between the measured lateral G and a calculated lateral G (from vehicle speed and a vehicle specification — e.g., tread) against a predetermined value.

I could not verify, from the references I was able to retrieve, a disclosure of this specific measured-vs-model-calculated lateral-G deviation test using the tread dimension. This is the one limitation for which my mapping is incomplete. Two caveats:

1. The general technique (deriving road friction from how the achieved lateral acceleration compares to the friction-limited maximum, and from vehicle-speed/model relationships) is a long-known practice reflected in US 5,332,300's discussion of computing μ, and US 5,275,475 teaches the parallel methodology of comparing computed transverse acceleration against measured transverse acceleration. A POSITA would likely view the lateral-G analogue as an obvious application of the same deviation-comparison methodology.
2. JPH 03-258650 (Toyota), cited in the family, is titled as a road-surface friction-coefficient detecting device and is the most likely reference to supply claim 6's specific test. Its text should be retrieved before making a final call. If it discloses a lateral-G-based friction estimate, claim 6 also falls.

As the record stands, claim 6 (and the claim-4 combination as a whole) is the most defensible subject matter in the patent.

Ground 7 — Claim 7

Claim 7 is the combination of Grounds 3 and 4 (low-μ + over/under-steer → the same damper trims). Given the literal dependency on claim 3 while reciting claim 4's steps, it would be construed either as depending from claim 4 (in which case it adds only the low-μ conditionality, i.e., it is obvious for the reasons of Grounds 3–4) or as internally inconsistent. Either way it adds no independent inventive weight.

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6. Consolidated KSR rationale

The KSR (550 U.S. 398) rationales that apply most cleanly:

1. Combining prior-art elements according to known methods to yield predictable results. Yaw-rate-error over/under-steer determination (US 4,761,022; DE 4123235) + front/rear damping trim (US 4,650,212) → a damper controller that trims front/rear damping in response to the diagnosed steer state. Each element does exactly what it was known to do.
2. Simple substitution of one known element for another. Brake-slip (DE 4123235), load-shift allotment (US 4,761,022), roll-stiffness distribution/rear steering (US 6,556,909) and damper force (US 4,650,212, US 4,555,126) were all interchangeable known actuators for adjusting the vehicle's yaw/steer balance. Selecting the damper is an obvious substitution.
3. Use of a known technique to improve a similar device in the same way. US 4,650,212 already coupled steering inputs to front/rear damping; adding the yaw-rate feedback path is the same technique applied to the same problem.
4. "Obvious to try" / finite number of predictable solutions. Once the goal is "correct under-steer/over-steer automatically," the design space is small: sense the yaw error, classify, act on the axle that needs restoring with a known actuator. The prior art identifies each step.
5. Design choice / sign-carrier equivalence. Choosing δ rather than yaw rate as the sign normalizer in claim 2 (Interchangeable known elements).

Objective evidence of non-obviousness: none of record. As established in the earlier sections of this analysis, the '537 patent was never asserted (no litigation, PTAB, ITC, or CAFC record found), it lapsed 2016-06-15 for nonpayment of maintenance fees, and no nexus-backed evidence of commercial success, long-felt need, or industry praise appears anywhere in the materials. Accordingly, no secondary consideration weighs against the § 103 conclusions above.

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7. Anticipated counter-arguments (and responses)

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8. Bottom line

Overall: Claims 1, 2, 3, 5 and 7 appear obvious over US 4,650,212 in view of US 4,761,022 and DE 4123235, with US 4,555,126 and US 5,332,300 as reinforcing secondary references. Claim 4's slipperiness-determination architecture is strongly suggested by US 5,332,300's express use of road-friction information in yaw-rate-based stability control; claim 6's specific lateral-G deviation test is the limitation on which a validity defense would most plausibly rest.

Confidence and limits. I retrieved and read substantive text for US 4,650,212, US 4,761,022, DE 4123235 C2 / US 5,341,297, US 5,332,300, US 5,275,475 and US 6,556,909. I did not retrieve text for JPH 03-258650, JP 3608445, US 5,032,997, JPH 07-89315, JPH 05-221213, JP 3131049, DE 40 10 277, DE 44 36 162 or US 5,931,887 — those are listed above by title (as recorded in the patent's family citations) only, and I have not attributed any disclosure to them. I also did not verify the exact U.S. filing date of US 6,556,909 (relevant to its precise pre-AIA § 102(e) date), only that it was cited by the examiner. The "Family Cites Families" list is Google Patents' aggregation of the family's citation lists and does not prove those documents were before the U.S. examiner.