Electrically Heated Catalyst Insulation Short Circuit Prevention
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Solution Overview
Problem
In electrically heated catalysts (EHCs) for internal combustion engines, conductive particulate matter (PM) deposits on insulating members, risking short circuits between the heating element and the case due to insufficient oxygen during engine operation, making it difficult to oxidize and remove PM.
Innovation Solution
A control device that electrically conducts the heating element after engine stoppage to heat the insulating member, ensuring sufficient oxygen is present in the exhaust gas for PM oxidation and removal, thereby preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulating member is provided between the heating element and the case, then short circuit prevention is improved, but PM deposition on the insulating member end causes reliability deterioration
Solution Approach 1:
The patent converts the harmful PM deposits into a beneficial oxidation process. By controlling the air-fuel ratio to be lean (excess air) during engine operation, the deposited PM on the insulating member is oxidized and removed. This transforms the harmful accumulation of conductive PM into a self-cleaning mechanism where the same PM deposits become fuel for oxidation, preventing short circuits without requiring additional active cleaning systems.
Solution Approach 2:
The patent changes the air-fuel ratio parameter from stoichiometric or rich conditions to lean conditions (excess air). This parameter change creates an oxidizing environment that prevents PM accumulation on the insulating member. The control unit adjusts the air-fuel ratio to maintain excess oxygen, which oxidizes PM deposits at the insulating member surface, thereby converting a potentially harmful accumulation into a controlled chemical process that maintains reliability.
2Productivity
If the air-fuel ratio is controlled at theoretical air-fuel ratio during engine operation, then combustion efficiency is improved, but oxygen insufficiency prevents PM oxidation
Solution Approach 1:
The patent deliberately changes the air-fuel ratio parameter from the theoretical stoichiometric ratio to a lean ratio with excess air. This parameter modification prioritizes PM oxidation capability over maximum combustion efficiency. The control unit maintains an air-fuel ratio with excess oxygen specifically to enable oxidation of PM deposits on the insulating member, accepting a trade-off in combustion efficiency to ensure reliability prevention.
Solution Approach 2:
The patent uses the excess air (which would otherwise be considered wasted oxygen) as a beneficial resource for oxidizing PM deposits. The lean air-fuel ratio creates an oxidizing atmosphere that converts harmful PM accumulation into a controlled oxidation process, where the excess oxygen serves dual purposes: maintaining combustion while simultaneously cleaning the insulating member surface.
3Temperature
If the heating element is electrically conducted during engine operation, then heating function is improved, but PM short circuit risk increases due to insufficient oxygen
Solution Approach 1:
The patent applies preliminary action by maintaining a lean air-fuel ratio with excess oxygen during engine operation before PM deposits become conductive enough to cause short circuits. This preventive measure ensures that PM is oxidized in advance, removing the harmful conductive layer before it can bridge the insulating member and cause a short circuit, thereby preventing the problem before it occurs.
Solution Approach 2:
The patent converts the potential harmful effect of PM deposition during heating operation into a beneficial oxidation process. By ensuring excess oxygen is present during engine operation, the PM deposits that form on the insulating member are continuously oxidized and removed, transforming what would be a harmful accumulation into a self-cleaning mechanism that maintains reliability during catalyst heating.
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
Effectively oxidizes and removes PM deposits on insulating members, preventing short circuits and ensuring the reliability and efficiency of the EHC system.
Implementation Method 1
a heating element that is heated by electric conduction to heat the catalyst by the heating
Implementation Method 2
an insulating member provided between the heating element and the case to insulate electricity
Implementation Method 3
electrically conducts the heating element after the operation of the internal combustion engine is stopped to heat the end of the insulating member, thereby oxidizing and removing a PM deposited on the end of the insulating member
Data Source
AI summary
A purpose of the present invention is to prevent a PM-caused short circuit between a heating element and a case in an electrically heated catalyst. The electrically heated catalyst is provided in an exhaust gas passage of an internal combustion engine the air-fuel ratio of which is controlled at a ratio near a theoretical air-fuel ratio at an operation time. The electrically heated catalyst includes a heating element that generates heat through electric conduction, a case that stores the heating element therein, and an insulating member sandwiched between the heating element and the case. According to the present invention, the heating element is electrically conducted after the operation of the internal combustion engine is stopped.