Evaporative Leak Diagnostics Using Vacuum Pump
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Solution Overview
Problem
Conventional evaporative leak diagnostics in fuel systems, particularly in hybrid vehicles, face challenges as they rely on natural engine vacuum, which may not be available during drive cycles, limiting the ability to perform integrity tests efficiently.
Innovation Solution
A diagnostic module with a pump, pressure sensor, and orifice is used to measure reference pressures and compare them to thresholds, allowing for evaporative leak testing independent of engine vacuum, enabling tests in both conventional and hybrid vehicles and accommodating multiple regulatory standards with a single orifice size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If natural engine vacuum is used to perform evaporative leak diagnostics, then the diagnostic can be performed using existing engine operation, but the diagnostic cannot be performed in hybrid vehicles during drive cycles when the engine is not running
Solution Approach 1:
A vacuum pump is introduced as an intermediary device to generate the necessary vacuum for leak diagnostics. The pump serves as a mediator that replaces the need for natural engine vacuum, enabling diagnostics to be performed independently of engine operation. This resolves the contradiction by providing a reliable vacuum source that works in both conventional and hybrid vehicles during drive cycles.
Solution Approach 2:
The diagnostic system performs self-service by generating its own vacuum requirement through an integrated vacuum pump. Instead of relying on the engine's natural vacuum (which may not be available), the system becomes self-sufficient by creating the necessary vacuum conditions internally, allowing leak diagnostics to be conducted at any time regardless of engine state.
2Productivity
If a pump is used to generate vacuum for leak diagnostics, then diagnostics can be performed independently of engine vacuum, but the system complexity increases
Solution Approach 1:
The vacuum pump is designed to serve multiple functions: it generates vacuum for leak diagnostics, and can potentially serve other vacuum-related functions in the vehicle system. This multi-functionality justifies the added complexity by maximizing the utility of the pump component, enabling frequent leak testing while reducing overall system complexity through consolidation of functions.
Solution Approach 2:
The vacuum pump is activated before the actual leak diagnostic measurement to establish the necessary vacuum conditions. This preliminary action ensures that the diagnostic can be performed accurately and frequently without waiting for natural engine vacuum to develop, thereby increasing productivity while the pump remains a dedicated component for this specific preparatory function.
3Adaptability or versatility
If multiple orifice sizes are used to meet various regulatory standards, then different leak thresholds can be tested, but the device complexity and calibration requirements increase
Solution Approach 1:
Instead of changing physical orifice sizes to meet different regulatory standards, the system changes the parameter of orifice flow resistance through a single variable orifice mechanism. This allows the same physical component to provide different flow characteristics by adjusting its opening degree, thereby complying with multiple regulatory standards while reducing device complexity and eliminating the need for multiple fixed orifice sizes.
Solution Approach 2:
The orifice is made dynamic rather than static, allowing its effective size to be adjusted during operation. This dynamic orifice can be controlled to provide different flow restrictions corresponding to different regulatory thresholds, enabling a single component to replace multiple fixed orifices and simplifying the overall device structure while maintaining versatility.
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 enables prompt and frequent evaporative leak testing after vehicle shutdown, improving diagnostic accuracy and frequency, and reducing the need for complex hardware adjustments, while ensuring compliance with various emission standards.
Implementation Method 1
A pump draws vacuum across a reference orifice (reference pull) to obtain a leak threshold
Implementation Method 2
the pump is operated to place the fuel system in a low pressure state
Implementation Method 3
measure a reference pressure across the orifice in the diagnostic module to provide a threshold
Data Source
AI summary
A method is provided for performing an evaporative leak diagnostic for a vehicle. A valve in a diagnostic module is commanded to a vent position. The valve connects a fuel system to atmosphere. A pump in the diagnostic module is operated to measure a reference pressure across an orifice in the diagnostic module to provide a threshold. The valve is commanded to a test position. The pump is operated to place the fuel system in a low pressure state. A series of pressures in the fuel system is measured. A diagnostic code is provided after comparing the series of pressures to the threshold.