Piston Ring Gap and Cylinder Bore Recess for Handheld Engine Starting

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Solution Overview

Problem

Handheld work apparatus with internal combustion engines face delays during starting due to slow gas escape from the combustion chamber, leading to inefficient engine operation and potential uncombusted fuel loss through escape grooves or channels.

Innovation Solution

The design incorporates a piston ring configured as an open ring with a gap, and recesses in the cylinder bore that bridge the piston rings, allowing controlled leakage between the combustion chamber and crankcase, avoiding direct connection to function openings, thereby facilitating delay-free starting without the need for a spring-starting device.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If escape grooves or channels are provided in the cylinder to connect the combustion chamber with the outlet, then the gas volume in the combustion chamber can reduce rapidly during starting, but uncombusted fuel can escape through the outlet and engine power is reduced

Engineering Contradiction:

Improvestarting delayVSAvoiduncombusted fuel escape

Core Design Contradiction:

Loss of timeVSObject-generated harmful factors

Solution Approach 1:

The escape function is segmented into multiple paths: a first escape path through the piston ring gap to the crankcase, and a second escape path through transfer channels to the combustion chamber. This segmentation allows controlled gas volume reduction during starting while preventing uncombusted fuel from escaping directly to the outlet, thus resolving the contradiction between fast starting and fuel loss.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The crankcase acts as an intermediary chamber between the combustion chamber and the external environment. Gas escapes from the combustion chamber to the crankcase through the piston ring gap, then to the outlet through transfer channels. This intermediary path controls the escape process, allowing rapid gas volume reduction during starting while maintaining proper fuel combustion and preventing direct fuel loss to the outlet.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the piston ring is configured as an open ring with a gap, then gas can escape from the combustion chamber to the crankcase, but the gap must be positioned to avoid direct connection to function openings

Engineering Contradiction:

Improvestarting speedVSAvoidpiston ring configuration

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The piston ring is configured as an open ring with a gap at a specific location (in the region of the inlet, above the lower edge of the inlet). This local configuration allows gas to escape to the crankcase during starting while the gap position prevents direct connection to function openings like the outlet. The localized gap placement optimizes the escape function without requiring complex additional structures.

Inventive Principle:

Principle #3Local quality

3Reliability

If a recess is formed in the cylinder bore to bridge the piston ring, then controlled leakage occurs between combustion chamber and crankcase, but the recess must be spaced to all function openings

Engineering Contradiction:

Improvestarting reliabilityVSAvoidcylinder bore structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The recess is formed in the cylinder bore at a predetermined position and spacing from all function openings (inlet, outlet, transfer channels) before the engine operates. This preliminary structural preparation ensures that during starting, the piston ring gap bridges the recess to create a controlled leakage path to the crankcase, while the spacing prevents direct connection to function openings. This preliminary configuration guarantees reliable starting without requiring complex active control mechanisms.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration ensures efficient starting and maintains good exhaust-gas values by allowing controlled gas escape, preventing uncombusted fuel from reaching the outlet and reducing compression loss during operation.

Implementation Method 1

The gas volume in the combustion chamber can escape, in part, to the crankcase via the bridging of the piston rings and the piston skirt

Methodology Applied

Scientific EffectGas escape through piston ring gap:

Implementation Method 2

The design incorporates a piston ring configuration with recesses and grooves in the cylinder bore that allow controlled leakage between the combustion chamber and crankcase

Methodology Applied

Scientific EffectControlled leakage:

Implementation Method 3

internal combustion engine

Methodology Applied

Scientific EffectCombustion: Combustion

Data Source

PatentUS8662047B2Handheld work apparatus

Publication Date: 2014.03.04 ANDREAS STIHL AG & CO KG

AI summary

A handheld work apparatus has an internal combustion engine (9, 9′, 9″) and a starter device (8). The internal combustion engine has a piston (10, 10″) which has at least one piston ring (37, 38). In order to avoid a delay when starting the engine, at least one recess is provided in the cylinder bore (26) which bridges the at least one piston ring (37, 38) in at least one position of the piston (10, 10′) and which has a distance (n, o, p) to all function openings of the engine (9, 9′, 9″) configured in the cylinder bore (26). To reduce the compression in the combustion chamber (25), the piston (10′) has only one piston ring (37) or two piston rings (37, 38) are provided having respective piston ring gaps (39, 40) defining an angle (β) which is up to approximately 45°.