Multi-Lift Valvetrain for Cylinder Deactivation Gas Exchange
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Solution Overview
Problem
Cylinder deactivation strategies in cam-driven valvetrains face challenges in gas exchange and internal residual management, leading to cycle-to-cycle charge-air intake differences and potential catastrophic failure of intake valves when exhaust valves are deactivated, limiting fuel efficiency, emission reduction, and combustion stability.
Innovation Solution
A multi-lift valvetrain system with switchable intake and exhaust cam-follower assemblies, featuring primary and secondary lift states for the exhaust valve, allows for exhaust re-breathe and heat transfer, and internal residual management through cam phasing, preventing intake valve opening into a positively pressured cylinder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the exhaust valve is deactivated preceding the intake valve opening event in a cylinder deactivation strategy, then fuel economy is improved by reducing pumping losses, but gas exchange between exhaust and intake valves becomes impossible causing cycle-to-cycle charge-air intake differences and potential catastrophic failure
Solution Approach 1:
The system dynamically switches between a single-lift mode (for normal operation) and a multi-lift mode (for deactivation transitions). The exhaust valve can be opened to different lift levels depending on the combustion cycle state, allowing controlled gas exchange during transitions while maintaining deactivation benefits during steady-state operation.
Solution Approach 2:
The exhaust cam is segmented into multiple lobes (first exhaust cam lobe for primary lift, second exhaust cam lobe for secondary lift) that can independently actuate the exhaust valve at different times. This segmentation enables selective opening of the exhaust valve to different degrees based on the combustion cycle phase, resolving the conflict between maintaining deactivation and preventing pressure buildup.
2Loss of substance
If the exhaust valve is deactivated preceding the intake valve opening event, then fuel consumption is reduced via de-throttling, but opportunities for reducing exhaust emissions via dilution are eliminated
Solution Approach 1:
The system dynamically controls exhaust valve lift based on combustion cycle state. During transitions from deactivated to active cycles, the exhaust valve is opened to a secondary lift level to enable controlled dilution of the intake charge with exhaust gases, reducing emissions while maintaining fuel efficiency benefits during steady-state deactivation.
3Loss of substance
If the exhaust valve is deactivated preceding the intake valve opening event, then fuel consumption is reduced via de-throttling, but combustion stability via heat addition is improved
Solution Approach 1:
The system dynamically adjusts exhaust valve operation based on combustion cycle detection. During deactivation transitions, the exhaust valve is opened to a secondary lift level to provide controlled heat addition from residual exhaust gases, improving combustion stability while maintaining the fuel consumption benefits of cylinder deactivation during steady-state operation.
4Reliability
If a multi-lift valvetrain system is implemented with primary and secondary lift states, then gas exchange dynamics are improved and catastrophic failures are prevented, but device complexity increases
Solution Approach 1:
The system combines multiple cam lobes (intake cam with first and second lobes, exhaust cam with first and second lobes) that can work together or independently. The cam follower assembly integrates multiple functions into a single component that can respond to different cam lobes, reducing the need for separate actuation mechanisms for each lift state.
Solution Approach 2:
The cam follower assembly serves multiple functions: it can be actuated by different cam lobes for different lift states, it automatically selects the appropriate cam lobe based on combustion cycle conditions, and it provides both primary and secondary exhaust valve opening functions through a single universal component design.
Data Source
AI summary
A cylinder deactivation system includes an intake cam follower assembly, an exhaust cam follower assembly, an exhaust cam, and a controller. The intake cam follower assembly is used to open an intake engine valve and is switchable to operate in one of an active state and a deactive state. The exhaust cam follower assembly is used to open an exhaust engine valve and is switchable to operate in one of a primary lift state and a secondary lift state. The exhaust cam includes a primary lift cam lobe and a secondary lift cam lobe and is used to actuate the exhaust cam follower assembly in the primary lift state and in the secondary lift state. The controller is used to open the exhaust engine valve during the deactive combustion cycle in advance of the opening of the intake engine valve that occurs during the subsequent active combustion cycle.