Two-Stroke Fuel Supply Partition Layout for Stable Mixture Flow

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Solution Overview

Problem

Existing fuel supply devices for two-stroke engines suffer from uncontrolled leaning of the fuel/air mixture when the throttle valve transitions from fully open to closed positions, leading to inefficiencies and operational disturbances.

Innovation Solution

A fuel supply device with a partition section that includes a central section and lateral sections upstream of the throttle valve, guiding the mixture flow away from connecting openings and minimizing exposure to abrupt pressure changes, allowing for seamless operation and reduced mixture entry into the air duct.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the partition section extends into the machining area to close the connecting opening, then the seal between throttle shaft and partition section is improved, but the device complexity increases due to separate partition section and complex sealing requirements

Engineering Contradiction:
Improveseal between throttle shaft and partition sectionVSAvoiddevice complexity
Core Design Contradiction:
ReliabilityVSDevice complexity

Solution Approach 1:

The partition section is merged with the base body of the fuel supply device to form an integral structure. This eliminates the need for separate partition sections and complex sealing arrangements between the throttle shaft and partition section, while still achieving the function of closing the connecting opening when the throttle valve is in the open end position.

Inventive Principle:
Principle #5Merging (Combining)

2Productivity

If the throttle valve is fully open, then the fuel flow is maximized, but the mixture may overflow into the air duct causing uncontrolled leaning

Engineering Contradiction:
Improvefuel flowVSAvoidmixture control
Core Design Contradiction:
ProductivityVSReliability

Solution Approach 1:

The partition section is designed with lateral sections that extend into the second area to preemptively guide the mixture flow away from the connecting openings before the throttle valve can cause uncontrolled leaning. This preliminary flow guidance prevents the harmful effect of mixture overflow into the air duct while maintaining full fuel flow capability.

Inventive Principle:
Principle #10Preliminary action

3Manufacturing precision

If the intake manifold section is machined beyond the throttle shaft bearing area, then the closure of throttle valve is improved, but the connecting opening between intake manifold wall and throttle valve is formed

Engineering Contradiction:
Improveclosure of throttle valveVSAvoidconnecting opening
Core Design Contradiction:
Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The connecting opening that forms as a result of machining the intake manifold section beyond the throttle shaft bearing area is converted from a harmful feature to a beneficial one. The lateral sections of the partition section utilize this opening to guide the mixture flow away from the air duct, transforming the potential source of uncontrolled leaning into a controlled flow path.

Inventive Principle:
Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentEP4119782B1Fuel supply device and two-stroke engine having a fuel supply device
Publication Date: 2026.02.25 ANDREAS STIHL AG & CO KG
  • EP4119782B1 patent drawingFigure 1~2
  • EP4119782B1 patent drawingFigure 3~6
  • EP4119782B1 patent drawingFigure 7~9

AI summary

A fuel supply device (20) has a base body (21) with an intake channel section (22) into which a main fuel inlet (24) opens. A throttle valve (25) is provided for controlling the free flow cross-section of the intake channel section (22), which is pivotably mounted about a pivot axis (45). The fuel supply device (20) has a partition section (27) which extends at least also upstream of the throttle valve (25) in the intake channel section (22) and which divides the intake channel section (22) into a mixture channel (18), into which the fuel inlet (23, 24) supplies fuel, and an air channel (19). The partition section (27) has a recess (48) in which the throttle valve (25) is at least partially located in an end position (52).The partition section (27) has a continuous mixture channel surface (41) facing the mixture channel (18) upstream of the recess (48). This surface has lateral sections (54) adjacent to the intake channel wall (56) and a central section (53) extending between the lateral sections (54). The lateral sections (54) have a separation edge (43) upstream of the throttle valve (25) for the flow in the mixture channel (18). The side (57) of the throttle valve (25) facing the mixture channel (18) in the end position (52) of the throttle valve (25) defines a reference plane (60) that divides the fuel supply device into a first area (71), in which the throttle valve (25) is located, and a second area (72). The lateral sections (54) extend at least directly upstream of the recess (48) into the second area (72) of the fuel supply device.