Pressureless Fuel Tank Venting for EVAP Canister Reverse Purge
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Solution Overview
Problem
Pressure-less fuel tanks in vehicles do not facilitate reverse purging of evaporative emissions canisters due to bellows expansion and contraction, which prevents vacuum-induced purging during diurnal temperature cycles, leading to potential hydrocarbon leaks and increased system complexity.
Innovation Solution
A method to convert a sealed variable volume fuel tank to a fixed-volume tank during cool-down hours by closing a valve at the atmospheric port and opening a fuel tank isolation valve, enabling vacuum-induced reverse purging of the evaporative emissions canister.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sealed variable volume fuel tank with bellows is used to maintain atmospheric pressure and eliminate pressure buildups, then pressure-related component degradation is reduced and hardware costs are decreased, but reverse purging of the EVAP canister cannot occur during diurnal cooling cycles
Solution Approach 1:
The system dynamically switches between two operational modes: during daytime, the bellows maintains variable volume to prevent pressure buildup; during nighttime cooling, the system transitions to fixed volume mode to enable reverse purging. This dynamic adaptation allows the system to achieve both pressure management and emissions reduction benefits at different times.
Solution Approach 2:
The system exploits the periodic diurnal temperature cycle to alternately enable and disable bellows operation. During cooling periods (night), reverse purging occurs naturally; during warming periods (day), the bellows maintains pressure equilibrium. This periodic exploitation of environmental cycles achieves both goals without continuous active control.
2Object-generated harmful factors
If a fixed-volume fuel tank is used to enable reverse purging during cooldown hours, then evaporative emissions are reduced and canister size can be minimized, but pressure and vacuum buildups occur during temperature cycles requiring complex venting hardware
Solution Approach 1:
The bellows acts as a dynamic volume adjustment mechanism that maintains atmospheric pressure in the fuel tank during daytime, eliminating the need for complex pressure relief valves, standoffs, and reinforcement structures required in fixed-volume systems. The system adapts its volume to accommodate temperature-induced pressure changes.
Solution Approach 2:
The system changes the volume parameter of the fuel tank using the bellows mechanism to maintain pressure equilibrium during daytime, then transitions to fixed volume during nighttime to enable reverse purging. This parameter change allows the system to avoid both pressure buildup issues and emissions problems simultaneously at different times.
3Reliability
If the bellows valve remains open during cooldown hours to maintain pressureless operation, then pressure management is maintained, but vacuum generation and reverse purging are prevented
Solution Approach 1:
The control system periodically closes the bellows valve during nighttime cooling hours to enable reverse purging, then reopens it during daytime to restore pressureless operation. This periodic switching allows the system to achieve both pressure management and emissions reduction benefits at appropriate times in the diurnal cycle.
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
Adapts the advantage of non-integrated refueling canister-only systems to sealed variable volume systems, facilitating reverse purging and reducing evaporative emissions without complex structural reinforcements.
Implementation Method 1
bellows expand and contract to minimize pressure generation in the tank, such as pressure vacuum generation due to ambient cooling
Implementation Method 2
The vacuum generated in the fuel tank pulls fresh air into the canister, purging stored fuel vapors
Implementation Method 3
the EVAP canister may adsorb depressurization fuel vapors and refueling fuel vapors
Data Source
AI summary
Methods and systems are provided for performing a reverse purge of an evaporative emissions canister in a vehicle with a sealed variable volume fuel tank. In one example, a method may comprise in response to an ambient temperature reducing during a diurnal temperature cycle, and further in response to the EVAP canister loaded with fuel vapors above a threshold, closing a valve positioned at an atmospheric port of the fuel tank and opening a fuel tank isolation valve. In one example, the fuel tank isolation valve may be in fluid communication between the fuel tank and the EVAP canister. In this way, it is possible to convert a sealed variable volume fuel tank to a vented pressurized fuel tank and initiate a reverse purge during the cooldown hours of the diurnal temperature cycle.