Fuel Control System with Electrically Actuated Valve for Precise Air-Fuel Ratio
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Solution Overview
Problem
Existing carburetors for two-cycle and four-cycle engines, particularly handheld engines, face challenges in efficiently controlling fuel and air mixtures, especially at lower engine speeds and idle conditions, due to limitations in air-fuel ratio control and sensitivity to fuel type, air leaks, and engine condition variations.
Innovation Solution
A charge forming device with a diaphragm-type fuel metering assembly and an electrically actuated valve that uses subatmospheric pressure to vary fuel flow, combined with a solenoid valve to control pressure pulses, allowing for precise adjustment of the air-fuel ratio by communicating negative pressure pulses to the fuel metering diaphragm, enabling leaner or richer fuel mixtures based on engine conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traditional carburetor is used for fuel metering, then the structure is simple and easy to manufacture, but the control precision of air-fuel ratio is poor especially at lower engine speeds and idle conditions
Solution Approach 1:
The patent replaces the purely mechanical fuel metering system with an electrically actuated solenoid valve that controls pressure pulses to the reference chamber. This electrical control mechanism enables precise adjustment of the air-fuel ratio through electronic signals, significantly improving measurement precision while accepting increased device complexity through the addition of the solenoid valve and control circuitry.
2Ease of operation
If a diaphragm-type carburetor is used to enable operation in any orientation, then the ease of operation is improved, but the sensitivity to fuel type variations and air leaks increases
Solution Approach 1:
The patent incorporates a reference chamber that receives pressure pulses from the main bore and communicates with the fuel chamber through a diaphragm. This feedback mechanism allows the system to automatically adjust fuel metering based on actual pressure conditions in the carburetor, compensating for variations in fuel type and detecting air leaks through pressure changes, thereby improving reliability while maintaining ease of operation in various orientations.
3Extent of automation
If an electrically actuated valve is added to control pressure pulses, then the control precision is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent uses a reference chamber as an intermediary between the main bore and the fuel chamber. The solenoid valve controls pressure pulses to this reference chamber, which then indirectly controls fuel metering through the diaphragm. This intermediary approach allows for automated control while managing complexity by using a relatively simple pressure chamber and diaphragm mechanism rather than directly controlling the fuel flow path.
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 solution provides improved control over the air-fuel ratio, enhancing engine performance and emissions by allowing for precise fuel adjustment across various operating conditions, including lower speeds and idle, while reducing corrosion and heat-related issues.
Implementation Method 1
a passage communicated with a subatmospheric pressure source and with the reference chamber
Implementation Method 2
a diaphragm with a first side that defines at least part of a fuel chamber from which fuel is provided to the main bore and a second side that defines at least part of a reference chamber
Implementation Method 3
an electrically actuated valve having an open position and a closed position, and wherein the valve at least substantially prevents communication of the pressure source with the reference chamber when the valve is in the closed position and permits communication of the pressure source with the reference chamber when the valve is in the open position
Data Source
AI summary
In at least some implementations, a charge forming device includes a body having a main bore, a fuel metering assembly including a diaphragm that defines at least part of a fuel chamber from which fuel is provided to the main bore and a reference chamber separate from the fuel chamber, a passage communicated with a subatmospheric pressure source and with the reference chamber, and an electrically actuated valve having an open position and a closed position, and wherein the valve at least substantially prevents communication of the pressure source with the reference chamber when the valve is in the closed position and permits communication of the pressure source with the reference chamber when the valve is in the open position to vary the rate of fuel flow from the fuel chamber.