Variable Turbine Nozzle Vane Control for Engine Braking Stability
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Solution Overview
Problem
Variable-nozzle turbochargers experience aerodynamic instability and accelerated wear during engine braking due to high dynamic pressure and pressure gradients caused by exhaust pulsation, leading to vane fluttering and vibrations.
Innovation Solution
A control method that initiates vane pivoting to a fully open position followed by actuating the exhaust flap to a further-closed position, then pivoting the vanes to a fully closed position against a hard stop, and maintaining this position until the exhaust flap opens, thereby stabilizing the vanes during engine braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the exhaust flap is closed to increase back-pressure for engine braking, then the braking torque on the vehicle is improved, but the variable vanes of the turbine nozzle experience aerodynamic instability and fluttering
Solution Approach 1:
The control system pivots the vanes to a predetermined position (fully open or intermediate) before the exhaust flap is closed, and maintains this position throughout the engine braking maneuver. This preliminary positioning prevents the vanes from being exposed to harmful pressure gradients and dynamic fluctuations that would otherwise cause aerodynamic instability and fluttering during flap closure.
Solution Approach 2:
The control system acts as an intermediary between the exhaust flap actuation and the variable vane positioning. By coordinating the vane position with the flap state through a control algorithm, the system mediates the interaction between these two components, ensuring that the vanes are protected from destabilizing pressure effects while the flap performs its braking function.
2Productivity
If the exhaust flap is closed during engine braking, then the engine braking effect is achieved, but the vanes experience accelerated wear due to high dynamic pressure and pressure gradients
Solution Approach 1:
The control system pre-positions the vanes to a protected state before the exhaust flap is closed, and maintains this position throughout the engine braking maneuver. This preliminary action shields the vanes from high dynamic pressure and pressure gradients that would otherwise cause accelerated wear, thereby extending component life while maintaining braking capability.
3Power
If the variable vanes are positioned to regulate exhaust gas flow, then the turbine power output is controlled, but the vanes become susceptible to aerodynamic instability when the exhaust flap closes
Solution Approach 1:
The control system determines the appropriate vane position based on engine operating conditions and exhaust flap state. When engine braking is detected (flap closing), the system pre-positions the vanes to a predetermined safe position that eliminates exposure to harmful pressure gradients, thereby preventing aerodynamic instability while allowing the flap to perform its braking function.
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
This method mitigates vane instability and reduces wear by positioning the vanes securely against a hard stop during high-pressure conditions, minimizing fluttering and vibrations.
Implementation Method 1
The exhaust gas flows from the chamber through the nozzle to the turbine wheel and the turbine wheel is driven by the exhaust gas
Implementation Method 2
The compressor receives ambient air through an inlet of the compressor housing and the air is compressed by the compressor wheel
Implementation Method 3
Changing the setting angles of the vanes has the effect of changing the effective flow area in the turbine nozzle, and thus the flow of exhaust gas to the turbine wheel can be regulated
Implementation Method 4
Closing the exhaust flap results in an increased back-pressure on the engine so that the engine exerts a braking torque on the vehicle drive train
Implementation Method 5
positioning the vanes securely against a hard stop during high-pressure conditions, minimizing fluttering and vibrations
Data Source
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AI summary
A control method for use in an engine braking maneuver for an internal combustion engine (ICE) system including a turbocharger having a variable-nozzle turbine (VNT), the ICE system further including an exhaust flap disposed in an exhaust line downstream of the variable-nozzle turbine. Prior to closing the exhaust flap, the VNT vanes are first parked in a fully open position. After the exhaust flap closes, the vanes are pivoted to a fully closed position and are continuously urged against a hard stop as long as the exhaust flap is closed. Termination of engine braking entails pivoting the vanes back to the fully open position, whereupon the exhaust flap is opened.