Parallel Canister Diagnostics for Heavy Duty Emissions
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Solution Overview
Problem
Heavy duty vehicles using non-ORVR systems face challenges with large fuel vapor storage canisters that restrict vapor flow and lead to increased evaporative emissions due to degraded adsorbent capacity in parallel canister configurations, where individual canister degradation is difficult to diagnose.
Innovation Solution
A method involving a canister working capacity diagnostic that measures exhaust gas air-fuel ratio while independently purging each fuel vapor storage canister, allowing for the identification of degraded canisters and preventing their use to reduce evaporative emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a large fuel vapor storage canister is used to match large fuel tanks, then the refueling vapor capacity is improved, but vapor flow restriction and back pressure increase
Solution Approach 1:
The patent divides the fuel vapor storage system into multiple smaller canisters arranged in parallel instead of using a single large canister. This segmentation provides equivalent total vapor capacity while reducing vapor flow restriction and back pressure in each individual canister, as vapors are distributed across multiple pathways.
2Stress or pressure
If multiple smaller canisters are arranged in parallel to reduce back pressure, then vapor flow is improved, but individual canister degradation becomes difficult to diagnose
Solution Approach 1:
The patent implements separate diagnostic pathways for each canister using individual vent valves and purge valves. This allows the control system to isolate and test each canister independently by controlling the flow paths, enabling accurate detection of individual canister degradation without interference from other canisters.
Solution Approach 2:
The patent uses feedback from oxygen sensors positioned in the exhaust system to monitor air-fuel ratio changes during diagnostic purging of each canister. The control system adjusts valve positions based on sensor feedback to accurately determine the working capacity of each individual canister.
3Object-generated harmful factors
If a canister working capacity diagnostic is performed to identify degraded canisters, then evaporative emissions are reduced, but system complexity and diagnostic time increase
Solution Approach 1:
The patent segments the diagnostic process to test each canister independently through controlled valve operations. By using individual vent valves and purge valves for each canister, the system can isolate and evaluate each canister's working capacity separately, accurately identifying degraded canisters without requiring complex external testing equipment.
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
Accurately identifies degraded canisters and reduces evaporative emissions by isolating and preventing the use of non-functional canisters, maintaining the refueling capacity and reducing emissions.
Implementation Method 1
a fuel vapor storage canister, also referred to herein as a 'canister,' that is packed with an adsorbent (e.g., activated carbon) that adsorbs and stores the vapors
Implementation Method 2
purge the stored vapors during a subsequent engine operation
Data Source
AI summary
Methods and systems are provided for an evaporative emissions control system for onboard refueling vapor recovery of a heavy duty vehicle. In one example, a method may include, in response to greater than a threshold change in a fuel level of a fuel tank fluidically coupled to at least two fuel vapor storage canisters of an evaporative emissions control system during a refueling event, performing a canister working capacity diagnostic on each of the at least two fuel vapor storage canisters by measuring an exhaust gas air-fuel ratio (AFR) while independently purging each of the at least two fuel vapor storage canisters. In this way, the working capacity of each fuel vapor storage canister may be separately assessed in order to more accurate identify degradation of the working capacity.