V-Type Engine Bank-to-Bank Torque Imbalance Correction
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Solution Overview
Problem
V-type engines with two-step variable valve lift systems experience significant cylinder bank-to-bank airflow imbalances in low lift mode, leading to torque imbalances that compromise stability, fuel economy, performance, and emissions.
Innovation Solution
A control system utilizing intake camshaft position sensors and exhaust gas oxygen concentration sensors to calculate and adjust intake camshaft positions, ensuring equal volumetric efficiencies across cylinder banks, thereby mitigating torque imbalances through targeted camshaft position shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a two-step variable valve lift system is used in low lift mode, then fuel economy is improved by reducing pumping work, but cylinder bank-to-bank airflow imbalance becomes more sensitive leading to torque imbalance
Solution Approach 1:
The system uses oxygen concentration sensors in the exhaust streams of both cylinder banks to continuously monitor airflow differences. The controller calculates volumetric efficiency corrections based on these oxygen readings and adjusts the intake camshaft positions accordingly. This closed-loop feedback mechanism dynamically compensates for airflow imbalances, allowing the engine to maintain stability while operating in fuel-efficient low lift mode.
Solution Approach 2:
The system changes the intake camshaft position parameter to correct airflow imbalances. By calculating the difference in volumetric efficiency between cylinder banks and applying appropriate camshaft position adjustments, the system modifies the timing and duration of valve events to equalize airflow distribution, thereby resolving the torque imbalance issue while maintaining low lift mode operation.
2Stability of the object's composition
If intake camshaft positions are adjusted to balance airflow, then torque imbalance is corrected, but system complexity increases due to additional sensors and control calculations
Solution Approach 1:
The controller performs multiple functions using the same sensor inputs: it monitors oxygen concentrations for both cylinder banks, calculates volumetric efficiency corrections, determines camshaft position adjustments, and executes the correction. The oxygen sensors serve dual purposes of monitoring combustion quality and enabling airflow balancing. This multi-functionality reduces the need for additional dedicated sensors while achieving torque balance.
Solution Approach 2:
The system uses its existing exhaust gas oxygen concentration measurements, already taken for combustion monitoring purposes, to self-diagnose and self-correct airflow imbalances. The controller leverages data already being collected from the exhaust sensors to calculate and implement camshaft position corrections, allowing the system to balance torque using its own operational data without requiring external intervention or additional specialized sensors.
Data Source
AI summary
An engine bank-to-bank airflow balancing technique includes calculating current and offset volumetric efficiencies of the engine and calculating a slope representing (i) a difference between the offset and current volumetric efficiencies and (ii) a difference between offset and current intake camshaft positions. Based on the respective exhaust gas oxygen concentrations, the technique involves calculating a volumetric efficiency correction corresponding to each cylinder bank and based on the slope and the volumetric efficiency corrections, calculating target intake camshaft position shifts. The technique further involves controlling offsets of the intake camshafts based on the target intake camshaft position shifts. After a predetermined number of target intake camshaft position shifts are determined and stored with respect to various combinations of engine speed and a ratio of intake manifold pressure to barometric pressure, final intake camshaft position shifts may be determined and utilized when determining the intake camshaft positions.