Variable Geometry Turbocharger Feed Forward Control
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Solution Overview
Problem
Traditional engine controllers using PID controls for variable geometry turbochargers require extensive calibration to prevent issues like compressor surge, turbo over-speed, and excessive exhaust manifold pressures, making it complex to achieve efficient engine operation while minimizing emissions.
Innovation Solution
A feed forward control method that uses an engine observer model to estimate engine states, calculate model corrections, and adjust turbocharger vane positions based on real-time sensor data and setpoint commands, integrating feedback actuator commands to optimize exhaust manifold pressure and flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PID controls are used for VGT, then sufficient boost and exhaust manifold pressure can be provided to prevent emissions, but excessive throttling occurs and engine efficiency is reduced
Solution Approach 1:
The control method uses feed forward control to calculate the desired VGT vane position based on predicted engine states and emissions requirements before the actual emissions problem occurs. This allows the system to proactively adjust the VGT to the optimal position that will achieve emissions targets without causing excessive throttling, rather than reacting after emissions problems or excessive pumping losses have occurred.
Solution Approach 2:
The control method incorporates feedback by continuously monitoring actual engine states (exhaust manifold pressure, mass flow rates) and comparing them with target values. The difference (error signal) is fed back to adjust the VGT position, ensuring emissions targets are met while minimizing pumping losses through iterative optimization.
2Reliability
If multiple protection mechanisms are added to prevent compressor surge, turbo over-speed, and high exhaust pressures, then system reliability improves, but control complexity and calibration effort increase significantly
Solution Approach 1:
The control method merges multiple protection functions into a single integrated control algorithm. Instead of having separate PID controllers and protection mechanisms for compressor surge, turbo over-speed, and exhaust pressure, the system uses one unified feed forward control approach that simultaneously manages all these parameters by optimizing the VGT position based on comprehensive engine state modeling and emissions requirements.
Solution Approach 2:
The control method creates a universal control algorithm that performs multiple functions: it controls VGT position for emissions, prevents compressor surge, avoids turbo over-speed, and manages exhaust pressure all through a single integrated approach based on engine state estimation and optimized control calculations, eliminating the need for separate specialized controllers for each function.
3Measurement precision
If feed forward control with engine observer model is used, then control accuracy and response speed improve, but computational requirements and model complexity increase
Solution Approach 1:
The control method introduces an engine observer model as an intermediary that estimates unmeasured engine states (mass flow rates, pressures, temperatures) based on available sensor data and physical models. This intermediary model enables accurate feed forward control calculations without requiring direct measurement of all engine parameters, reducing sensor complexity while improving state estimation accuracy.
Data Source
AI summary
A variable geometry turbocharger control method includes monitoring parameters of an engine using a plurality of sensors and generating engine state estimates using an engine observer model. The engine observer model represents the intake manifold volume, the exhaust manifold volume, and the charge air cooler volume. The engine state estimates are based on the monitored engine parameters from the plurality of sensors. The method also includes calculating a turbine intake correction factor based on the differences between the measured engine states and the engine state estimates and inputting the turbine intake correction factor to the engine observer model. The method further includes determining a desired turbocharger vane position based on setpoint commands, the monitored engine parameters, the turbine intake correction factor, and the engine state estimates. The method additionally includes adjusting positions of the vanes of the variable geometry turbocharger based on the desired turbocharger vane position.