Variable Valve Actuation for Turbocharged Engine Transient Response
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Solution Overview
Problem
Turbocharged diesel engines experience poor acceleration, particularly from idle or low engine speeds due to 'turbo-lag' caused by the time delay in filling the intake manifold with fresh air, limiting fuel delivery and resulting in reduced engine performance and increased emissions.
Innovation Solution
A method involving shifting the internal combustion engine from a stationary to a transient mode by closing the EGR valve and repositioning the VGT turbo unit's guide vanes, along with increasing the duration of valve overlap in the cylinder head to enhance air flow and accelerate the turbine, using a system with cam lobes and rocker arms actuated by hydraulic, electromagnetic, or air pressure circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the turbocharger is used to increase power output and decrease fuel consumption, then the engine efficiency is improved, but the acceleration performance deteriorates due to turbo-lag
Solution Approach 1:
The system performs preliminary action by pre-positioning the guide vanes in the VGT turbo unit to an optimal angle before transient conditions occur. When transient mode is detected, the vanes are already near the optimal position, eliminating the delay associated with adjusting from a closed or suboptimal position. This preliminary preparation of the turbocharger geometry enables rapid air supply response during acceleration.
Solution Approach 2:
The system implements dynamics by making the valve overlap duration variable rather than fixed. The camshaft system dynamically adjusts the overlap between inlet and outlet valve opening times based on operating conditions. During transient modes, increased overlap duration enhances air flow into the cylinder, improving acceleration response while maintaining the benefits of turbocharging during steady-state operation.
2Object-generated harmful factors
If the EGR valve is opened to reduce NOx emissions, then the emission characteristics are improved, but the air supply to the intake manifold deteriorates
Solution Approach 1:
The system dynamically adjusts the EGR valve position based on transient detection. During transient modes when acceleration is required, the EGR valve is closed or minimized to maximize fresh air supply to the intake manifold. During steady-state operation, the EGR valve is opened to the optimal position for emission reduction. This dynamic control allows the system to optimize both air supply and emission characteristics according to operating conditions.
3Power
If the fuel delivery is increased to satisfy torque demand, then the power output is improved, but the air-to-fuel ratio deteriorates below the smoke threshold
Solution Approach 1:
The system performs preliminary action by detecting transient conditions before full torque demand is applied and pre-adjusting the valve overlap duration and EGR valve position to optimize air supply. This preliminary preparation ensures that when fuel delivery is increased to satisfy torque demand, sufficient air is already available in the intake manifold to maintain the air-to-fuel ratio above the smoke threshold, enabling full power output without visible smoke.
Solution Approach 2:
The system uses feedback by continuously monitoring engine operating conditions and adjusting the valve overlap duration and EGR valve position accordingly. During transient modes, the feedback control increases overlap duration to enhance air flow, ensuring that fuel delivery can be increased to meet torque demand while maintaining proper air-to-fuel ratio. This closed-loop control prevents the air-to-fuel ratio from dropping below the smoke threshold.
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 approach improves engine response and acceleration, particularly for diesel engines, by optimizing air flow and reducing turbo-lag, thereby enhancing engine performance and reducing emissions.
Implementation Method 1
switching said secondary rocker arm between at least two different positions with a hydraulic circuit
Implementation Method 2
switching said secondary rocker arm between at least two different positions with an electromagnetic circuit
Implementation Method 3
switching said secondary rocker arm between at least two different positions with an air pressure circuit
Implementation Method 4
providing a first cam lobe on a rotatable camshaft for interacting with a main rocker arm
Data Source
AI summary
A method for reducing turbolag in a turbocharged internal combustion engine includes demanding torque for shifting the internal combustion engine from a stationary engine mode to a transient engine mode, closing an exhaust gas recirculation (EGR) valve during the transient engine mode, repositioning guide vanes of a Variable Geometry Turbine (VGT) turbo unit from a first position when in the stationary engine mode to a second position when in the transient engine mode, increasing a duration of overlapping of at least one inlet valve and at least one outlet valve provided in a cylinder head of the internal combustion engine from as first duration when in the stationary mode to a second duration when in the transient mode for increasing the amount of air flowing from an inlet manifold to an exhaust manifold and thereby increasing acceleration of a turbine of the VGT turbo unit.