Engine Idle-Stop Restart Piston Positioning
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Solution Overview
Problem
Existing engine idle-stop systems face challenges in accurately determining the engine position and aircharge estimation during restarts, leading to fuel consumption degradation and increased hydrocarbon emissions due to uncertainties in initial engine position, air mass, temperature, and residual gas fraction.
Innovation Solution
The method involves selecting a piston position for the first firing cylinder that is retarded from the exhaust valve closure and advanced from the intake valve closure, with a shorter valve overlap period and retarded intake valve closing timing, to reduce positioning errors and improve aircharge estimation accuracy during engine restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine is stopped at a desired position to improve starting during restart, then the repeatability of engine starts is improved, but uncertainties in determining the actual initial engine position, air mass, temperature, and residual gas fraction lead to inaccurate aircharge estimates
Solution Approach 1:
The system performs preliminary positioning of the piston to a specific crankshaft position range before the first combustion event during restart. This preliminary action ensures that the piston is positioned retarded from exhaust valve closure and advanced from intake valve closure, creating optimal conditions for accurate aircharge estimation and reliable combustion.
Solution Approach 2:
The system adjusts valve timing parameters, specifically retarding the intake valve closing timing and reducing the valve overlap period. These parameter changes optimize the cylinder conditions for aircharge estimation by controlling the amount of fresh air charge and residual gas composition in the cylinder at the time of measurement.
2Reliability
If the fuel injection amount is biased rich to compensate for position and aircharge estimate errors, then the reliability of combustion during restart is improved, but fuel consumption increases
Solution Approach 1:
The system replaces the conventional approach of using rich fuel mixture to compensate for uncertainties with a precision positioning and measurement approach. By accurately controlling piston position and measuring cylinder conditions, the system can determine accurate aircharge estimates without needing to add excess fuel, thus maintaining combustion reliability while reducing fuel consumption.
3Stability of the object's composition
If frequent engine restarts are performed with biased fuel-rich injection, then combustion stability during restart is maintained, but hydrocarbon emissions increase
Solution Approach 1:
The system replaces the use of rich fuel mixtures with precise piston positioning and accurate aircharge measurement. By knowing the exact cylinder conditions (piston position, air charge mass, temperature, residual gas fraction), the system can calculate the precise fuel injection amount needed for complete combustion, thereby maintaining combustion stability while minimizing hydrocarbon emissions from unburned fuel.
Data Source
AI summary
Methods and systems are provided for controlling a vehicle system including an engine that is selectively deactivated during engine idle-stop conditions and selectively reactivated during engine restart conditions. One example method comprises, during an engine restart from an idle stop, performing a first combustion event in a cylinder with a piston at an engine crankshaft position that is after a crankshaft position at which said cylinder's exhaust valve opens, and before a crankshaft position at which the cylinder's intake valve closes, during a cycle of said cylinder. In this way, inaccuracies in cylinder aircharge estimation may be reduced, thereby also reducing air-fuel ratio errors and improving the quality and repeatability of engine restarts.