Multi-level Skip Fire Engine Control for NVH Reduction
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Solution Overview
Problem
Skip fire engine control systems face challenges in reducing noise, vibration, and harshness (NVH) to an acceptable level, which has hindered their widespread adoption despite potential fuel efficiency gains, as existing solutions fail to effectively manage the wide range of operating conditions and resonance issues.
Innovation Solution
A multi-level skip fire engine control system that uses a camshaft with multiple lobes to adjust air charges in cylinders, allowing for selective firing and deactivation of working chambers, and independent control of intake valves to achieve varying torque outputs, thereby reducing NVH and improving fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If skip fire engine control is implemented to improve fuel efficiency, then fuel economy is improved, but noise, vibration and harshness (NVH) increases
Solution Approach 1:
The camshaft is made axially movable between multiple positions, allowing dynamic adjustment of cam lobe engagement with intake valves. This enables the engine to transition between different firing patterns (all cylinders firing, selective cylinder firing, or complete cylinder deactivation) based on operating conditions, thereby optimizing fuel economy while managing NVH levels through real-time adaptability
Solution Approach 2:
The system changes the engagement parameter of cam lobes with intake valves by axially positioning the camshaft at different levels. At a first axial position, all cylinders receive full air charges; at a second axial position, selected cylinders receive reduced or zero air charges. This parameter change enables flexible control of torque output and NVH characteristics while maintaining fuel efficiency
2Object-affected harmful factors
If camshaft is axially shifted to adjust air charges for NVH reduction, then NVH is reduced, but device complexity increases
Solution Approach 1:
Multiple cam lobes for different cylinders are merged into a single axially movable camshaft structure. This unified design allows simultaneous control of multiple intake valves through one component, reducing the need for separate actuators for each cylinder while enabling coordinated NVH management across the engine
Solution Approach 2:
The axially movable camshaft serves multiple functions: it controls air charge delivery to all cylinders, enables selective cylinder deactivation, and provides mechanical means for NVH management. This multi-functionality eliminates the need for additional dedicated NVH control mechanisms, thereby limiting the increase in device complexity
3Adaptability or versatility
If selective firing of cylinders is implemented to deliver desired torque, then torque control flexibility is improved, but manufacturing complexity increases
Solution Approach 1:
The camshaft is segmented into multiple cam lobes, each associated with a specific cylinder or group of cylinders. This segmentation allows independent control of air charge delivery to different cylinders through selective axial positioning, enabling flexible torque management while using a single manufacturable camshaft component rather than multiple separate components
Data Source
AI summary
In various aspects, internal combustion engines, engine controllers and methods of controlling engines are described. The engine includes a camshaft and a two cylinder sets. Cylinders in the first are deactivatable and cylinders in the second set may be fired at high or low output levels. The air charge for each fired working cycle is set based on whether a high or low torque output is selected. In some implementations, the camshaft is axially shiftable between first and second positions. First cam lobes are configured to cause their associated cylinders to intake a large air charge during intake strokes that occur when the camshaft is in the first position. Second cam lobes for cylinders in the second set cause their associated cylinders to intake a smaller air charge when the camshaft is in the second position. Second cam lobes for cylinders in the first set deactivate their associated cylinders.