Variable Event Valvetrain Control During Engine Stop-Start
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Solution Overview
Problem
Existing methods for controlling intake and exhaust valve operation in internal combustion engines during starting and stopping fail to consider combustion stability, leading to increased engine emissions, misfires, and reduced catalyst efficiency due to oxygen being pumped through the engine, which cools the catalyst and occupies reduction sites.
Innovation Solution
A method that adjusts valve lift and fuel flow in a variable event valvetrain to reduce cylinder air charge below a predetermined level during engine stopping and increases valve lift during starting, minimizing oxygen flow to the catalyst and ensuring consistent combustion, thereby reducing emissions and improving catalyst efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If valve lift is reduced during engine stopping to control engine speed, then engine speed is reduced in a controlled manner, but combustion stability is compromised leading to misfires and increased emissions
Solution Approach 1:
The patent dynamically adjusts valve lift as a variable parameter during engine stopping and starting sequences. By changing valve lift from a fixed value to a dynamic parameter that responds to engine operating conditions, the system achieves controlled engine speed reduction while maintaining combustion stability through real-time optimization of the valve timing parameter.
Solution Approach 2:
The patent implements feedback control by monitoring engine operating parameters during stopping and starting sequences. The system uses this feedback to adjust valve lift in real-time, ensuring that combustion stability is maintained while achieving controlled engine speed reduction. The feedback mechanism allows the system to adapt valve lift to actual engine conditions rather than following a fixed schedule.
2Device complexity
If constant valve lift command is used during engine starting, then valve operation is simplified, but oxygen is pumped through the engine cooling the catalyst and reducing catalyst efficiency
Solution Approach 1:
The patent transitions from a static, fixed valve lift command to a dynamic valve lift control strategy. During engine starting, the system dynamically adjusts valve lift based on engine speed and operating conditions, preventing excessive oxygen flow to the catalyst while maintaining controlled combustion. This dynamic approach eliminates the harmful effect of catalyst cooling without requiring complex multi-valve mechanisms.
Solution Approach 2:
The patent applies preliminary action by pre-adjusting valve lift before and during engine starting sequences. The system anticipates the oxygen pumping effect and proactively modifies valve timing to prevent excessive oxygen flow to the catalyst. This preliminary adjustment ensures that when combustion occurs, the catalyst is not cooled or oxygenated in a way that reduces its efficiency.
3Device complexity
If fuel flow is not adjusted during valve lift reduction, then fuel control is simplified, but misfires increase due to insufficient air charge for stable combustion
Solution Approach 1:
The patent coordinates changes in multiple parameters including valve lift and fuel flow during engine stopping and starting. By adjusting fuel flow in conjunction with valve lift reduction, the system maintains the appropriate air-fuel ratio for stable combustion even when cylinder air charge is reduced. This coordinated parameter adjustment prevents misfires while avoiding excessive complexity in the control system.
Solution Approach 2:
The patent uses feedback control to monitor combustion conditions and adjust fuel flow accordingly during valve lift modification. The system detects when combustion stability is compromised due to reduced air charge and automatically adjusts fuel flow to maintain optimal combustion conditions. This feedback mechanism ensures reliable combustion while keeping fuel control manageable through automated adjustment rather than complex manual coordination.
Data Source
AI summary
A method for controlling a variable event valvetrain during engine start and stop is presented. According to the method, valve lift and/or timing can be adjusted to reduce the amount of oxygen pumped into an exhaust gas after treatment system. The method can reduce engine emissions, at least during some conditions, since there may be less oxygen available to alter the operating state of the exhaust gas after treatment system.