Obviousness

Here's an analysis of the obviousness of US patent 11143120 under 35 U.S.C. § 103, identifying combinations of prior art references and the motivation for combining them, based on the provided patent text and its listed priority documents as prior art.

For this analysis, US10221780B2 ("Dual fuel lockout switch for generator engine") and US10697398B2 ("Batteryless dual fuel engine with liquid fuel cut-off") are considered prior art as they are cited as priority documents for US11143120 and establish a relevant prior art date of 2015-06-12. These patents likely disclose the basic elements of multi-fuel engines, fuel lines, and cutoff solenoids. The "Background of the Invention" section of US11143120 itself highlights known problems in existing dual-fuel systems, which provides strong motivation for a person having ordinary skill in the art (POSA) to seek solutions. A POSA in this field would be an engineer or technician familiar with small internal combustion engines, fuel systems, and generator design.

Analysis of Independent Claim 1: Multi-Fuel Engine with Timing Circuits

Claim 1: "A multi-fuel engine comprising: an engine operable on a liquid fuel and a gaseous fuel; a carburetor attached to an intake of the engine to mix air and fuel and connect a liquid fuel source to the intake, the carburetor comprising a float bowl; a liquid cutoff solenoid coupled to open and close a liquid fuel path to the engine; a gaseous cutoff solenoid coupled to open and close a gaseous fuel source to the engine; a switch selectively coupling a power source to the liquid cutoff solenoid and the gaseous cutoff solenoid to open and close the liquid fuel path and the gaseous fuel path; and one or more timing circuits electrically coupled to the liquid cutoff solenoid and the gaseous cutoff solenoid that operate to control an actuation time of the liquid cutoff solenoid and the gaseous cutoff solenoid."

• Prior Art Combination: US10221780B2 or US10697398B2, combined with general knowledge of electronic timing circuits.
• Elements Disclosed by Prior Art (e.g., US10221780B2 or US10697398B2, or general knowledge): Multi-fuel engines (e.g., dual-fuel generators), carburetors with float bowls, liquid and gaseous fuel cutoff solenoids, and switches to select between fuel sources are all explicitly or implicitly taught as known in the background of US11143120 and would be present in the mentioned priority documents. The "Background of the Invention" states, "Certain generators are configured to operate as 'dual fuel' generators... These generators are driven by an internal combustion engine that is configured to operate on either liquid fuel or an alternative fuel" and mentions a "first fuel line for liquid fuel and a second fuel line for gaseous fuel". The patent further describes "electrical fuel switch 54 for selecting a desired fuel to the engine" and "electro-mechanical valve system 76 that includes a carburetor cutoff solenoid 94, gasoline cutoff solenoid 96, and a LPG cutoff solenoid 98".
• Distinguishing Feature of Claim 1: The inclusion of "one or more timing circuits electrically coupled to the liquid cutoff solenoid and the gaseous cutoff solenoid that operate to control an actuation time of the liquid cutoff solenoid and the gaseous cutoff solenoid."
• Motivation to Combine: The "Background of the Invention" in US11143120 clearly articulates a problem in existing dual-fuel systems: "during cross-over switching between the fuel sources the engine can experience overly rich air-fuel ratio. This is particularly problematic when switching from a liquid fuel to a gaseous fuel because carburetors have a fuel bowl containing fuel that is drawn into the engine even after the liquid fuel source is cut-off. Therefore, for a period of time, the engine is running on both liquid and gaseous fuels causing an overly rich fuel mixture. Further, such simultaneous delivery of fuel from the first fuel line and the second fuel line, even if for a brief time, may make the engine hard to start and lead to unstable operating conditions".
  A POSA would be highly motivated to solve this known problem of "overly rich air-fuel ratio" and "simultaneous delivery of fuel" during fuel changeover, which leads to "hard starting, rough running, and unstable operating conditions". Introducing timing control for the solenoids would be a logical and predictable solution to precisely manage the opening and closing sequences, thereby preventing or minimizing the undesirable fuel overlap. The use of "adjustable rheostats or predefined electronic delay circuits" for introducing time delays or adjustments in control systems is a well-known engineering technique in electromechanical applications. Therefore, modifying an existing dual-fuel engine (as disclosed in US10221780B2 or US10697398B2) with standard timing circuits to address this known problem would be obvious to a POSA.

Analysis of Independent Claim 12: Multi-Fuel Generator with Off-Board Fuel Regulator System

Claim 12: "A multi-fuel generator and fuel delivery system comprising: a multi-fuel internal combustion engine configured to operate on a liquid fuel supplied from a liquid fuel source through a liquid fuel line and a gaseous fuel supplied from a pressurized fuel source through a gaseous fuel line; an alternator driven by the multi-fuel internal combustion engine; and a fuel regulator system located off-board the generator and comprising: a primary pressure regulator coupled to a service valve of the pressurized fuel source to regulate fuel supplied from the pressurized fuel source to a reduced pressure, and a secondary pressure regulator coupled to the primary pressure regulator to regulate fuel supplied from the primary pressure regulator to a desired pressure for delivery through the gaseous fuel line to operate the engine."

• Prior Art Combination: General knowledge of multi-fuel generators, two-stage gaseous fuel regulators, and design considerations for compact and cost-effective devices.
• Elements Disclosed by Prior Art (General Knowledge): Multi-fuel generators with engines driving alternators and operating on liquid and pressurized gaseous fuels are known (e.g., as exemplified by the general context of US11143120 and its priority documents). Gaseous fuel systems typically require pressure regulation, and two-stage pressure regulators are commonly used for pressurized fuels like LPG to safely and effectively reduce fuel pressure to the engine's operating requirements. The patent states, "Fuel regulator system 56 includes a primary pressure regulator 64 coupled to pressurized fuel container 50 and a secondary pressure regulator 66".
• Distinguishing Feature of Claim 12: The "fuel regulator system located off-board the generator."
• Motivation to Combine: US11143120 explicitly states the motivation for this arrangement: "secondary pressure regulator 66 is mounted off-board the generator to reduce size and cost of the generator". Reducing the size and cost of a product, particularly a portable generator, is a fundamental and often-sought design goal in engineering. A POSA would be motivated to achieve these benefits by moving bulky or heavy components that do not require integral mounting, such as the fuel regulator system, off-board the main generator unit. This would be a routine design optimization based on known desirable outcomes. Thus, combining a known multi-fuel generator with a standard two-stage gaseous fuel regulator system and locating it off-board to achieve recognized advantages of reduced size and cost would be obvious.

Analysis of Independent Claim 18: Carburetor with Main and Idle Circuit Cutoff Solenoid

Claim 18: "A carburetor for use in a multi-fuel internal combustion engine, the carburetor comprising: a throat in which fuel and air are mixed in throat to provide an air-fuel mixture for the multi-fuel internal combustion engine; a valve located in the throat to provide a choke and throttle for the multi-fuel internal combustion engine; a float bowl to hold liquid fuel; a main fuel circuit positioned downstream from the float bowl and extending from the float bowl to the throat; an idle fuel circuit that provides a flow path to the throat downstream of the throttle to run the engine at idle; and a carburetor cutoff solenoid configured to selectively control fuel flow through the main fuel circuit and the idle fuel circuit."

• Prior Art Combination: A standard carburetor (general knowledge) used in multi-fuel engines, combined with the knowledge of the fuel overlap problem during switching.
• Elements Disclosed by Prior Art (General Knowledge): The core components of a carburetor—throat, choke/throttle valve, float bowl, main fuel circuit, and idle fuel circuit—are all standard and well-known in internal combustion engine technology. Multi-fuel engines often adapt existing carburetor designs.
• Distinguishing Feature of Claim 18: A "carburetor cutoff solenoid configured to selectively control fuel flow through the main fuel circuit and the idle fuel circuit."
• Motivation to Combine: The "Background of the Invention" of US11143120 specifically identifies the problem: "This is particularly problematic when switching from a liquid fuel to a gaseous fuel because carburetors have a fuel bowl containing fuel that is drawn into the engine even after the liquid fuel source is cut-off. Therefore, for a period of time, the engine is running on both liquid and gaseous fuels causing an overly rich fuel mixture". This problem is particularly acute with the idle fuel circuit. The patent further clarifies that while "gasoline cutoff solenoid 96 prevents drawing gasoline through the idle fuel circuit after carburetor cutoff solenoid 94 closes the main fuel circuit," a more direct solution is preferred. The patent describes that "in another embodiment of the invention, carburetor cutoff solenoid 94 is configured to control fuel flow through both main fuel circuit 152 and idle fuel circuit 158. For instance, idle fuel circuit 158 may branch off from main fuel circuit 152 with carburetor cutoff solenoid 94 actuating to block fuel flow into both circuits".
  A POSA faced with the known problem of residual liquid fuel from the float bowl (especially through the idle circuit) causing an overly rich mixture during a fuel switchover would be motivated to ensure a complete cutoff of liquid fuel from all paths within the carburetor. Modifying a standard carburetor to integrate a cutoff solenoid that effectively blocks both the main and idle fuel circuits is a straightforward and logical engineering solution to directly address and prevent this known issue.