Engine Stop-Start NVH Control via Variable Valve Timing
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Solution Overview
Problem
Existing engine stop/start systems face challenges in achieving smooth and fast shutdowns without noise, vibration, and harshness (NVH) issues, while also ensuring rapid and effective restarts, particularly due to conflicts between closed and open throttle shutdown methods which affect air charge and crankshaft rotation.
Innovation Solution
The implementation of a method using variable valve systems to control cylinder air charge by adjusting poppet valve lift, duration, and timing, fully opening the throttle at the beginning of shutdown to maximize manifold pressure, then reducing it, and finally maximizing it again to prevent engine shake and ensure rapid restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the throttle is closed during engine shutdown to reduce NVH, then noise and vibration characteristics improve, but the engine shutdown time increases and restart performance deteriorates
Solution Approach 1:
The engine shutdown process is divided into multiple phases: an initial phase where the throttle remains open to maintain manifold pressure and achieve rapid shutdown, followed by a subsequent phase where the throttle closes to improve NVH characteristics. This temporal segmentation allows each phase to optimize for its specific objective without compromising the other.
Solution Approach 2:
The throttle is kept open in advance during the initial shutdown phase to maintain high manifold pressure, ensuring that cylinders have sufficient air charge for rapid engine cessation. This preliminary action of maintaining pressure before the throttle closes enables the engine to stop quickly without waiting for pressure depletion.
2Productivity
If the throttle is opened during engine shutdown to maintain manifold pressure, then restart performance improves, but NVH characteristics worsen due to increased vibration and shake
Solution Approach 1:
The throttle operation follows a periodic pattern: initially open to maintain pressure for rapid shutdown and good restart potential, then closed after a predetermined period or when specific conditions are met to reduce vibration. This time-based control strategy allows the system to transition from a performance-optimized state to a comfort-optimized state.
Solution Approach 2:
The throttle position is dynamically adjusted during the shutdown process rather than maintaining a fixed position. The throttle transitions from fully open to closed based on real-time engine conditions, manifold pressure levels, and timing criteria, allowing the system to adaptively balance restart performance with NVH reduction.
3Loss of energy
If the engine shuts down rapidly to maximize zero fuel use period, then emissions reduction benefit increases, but the crankshaft may reverse rotation causing pinion clash on restart
Solution Approach 1:
The control system continuously monitors engine speed, crankshaft position, and manifold pressure during shutdown. Based on this feedback, the system determines the optimal time to close the throttle and can detect approaching reverse rotation, allowing it to adjust the restart timing or throttle control to prevent pinion clash while maintaining rapid shutdown benefits.
Solution Approach 2:
The system takes preliminary action by closing the throttle at a predetermined time or when specific pressure thresholds are reached, before reverse rotation can occur. This preventive measure counteracts the potential harmful effect of crankshaft reversal, ensuring reliable restart without requiring delay mechanisms.
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 allows for a rapid, smooth engine shutdown with minimal NVH, eliminating rocking motion and enabling quick restarts without starter motor clash, while maintaining high air charges for efficient torque production.
Implementation Method 1
controlling the air charge to cylinders (1) of the engine by means of poppet valves (5) of the engine
Implementation Method 2
fully opening a throttle of said engine inlet at a beginning of engine shutdown so as to maximise available manifold pressure
Implementation Method 3
a cylinder predicted to stop on a compression stroke has a comparatively full air charge on the respective inlet stroke
Implementation Method 4
a cylinder predicted to stop on a power stroke has a reduced air charge
Data Source
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AI summary
Aspects of the present invention relate to methods of stop/start of an internal combustion engine provided with a CVVL system; also a control unit and a vehicle for employing the methods.