Multimode Engine Valvetrain with Negative Valve Overlap
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Solution Overview
Problem
Current engine technologies face challenges in improving low load performance, particularly in spark ignition combustion engines, due to issues like pumping loss, combustion instability, and limited operation range, which affect fuel efficiency and emissions.
Innovation Solution
Implementing a negative valve overlap (NVO) mode with early exhaust valve closing to increase in-cylinder gas temperature for improved fuel vaporization and mixing, and transitioning between spark ignition (SI) and low temperature combustion (LTC)-spark assisted (SA) modes based on predefined conditions, using continuously variable valve duration and timing mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If throttling is used to control engine load in SI combustion engines, then engine load can be regulated, but pumping loss increases and combustion efficiency decreases at low loads
Solution Approach 1:
The patent changes the valve timing parameters (exhaust valve closing timing and intake valve opening timing) to create negative valve overlap, which compresses the air charge and raises in-cylinder temperature and pressure without requiring throttle restriction, thereby reducing pumping loss while maintaining load control capability
Solution Approach 2:
The patent implements dynamic mode transition between SI and LTC combustion modes based on operating conditions, allowing the engine to adaptively switch combustion strategies to optimize efficiency across different load ranges while minimizing pumping losses
2Loss of energy
If external EGR is used to reduce throttling requirement, then pumping loss decreases, but combustion instability increases
Solution Approach 1:
The patent changes the combustion mode from SI to LTC by adjusting combustion temperature and pressure parameters, which allows for stable combustion with high EGR rates by fundamentally altering the combustion chemistry and heat release characteristics
Solution Approach 2:
The patent uses a small amount of direct injection fuel as an intermediary to initiate and stabilize combustion in the high EGR environment, where the pilot injection provides reliable ignition kernel formation that stabilizes the overall combustion process
3Loss of energy
If variable valve timing and lift are used to increase intake pressure, then pumping loss decreases, but operation range is limited
Solution Approach 1:
The patent changes the combustion mode parameter (from SI to LTC) which fundamentally alters the combustion characteristics and allows the engine to operate efficiently across a broader range of loads and speeds, overcoming the operation range limitations of variable valve timing alone
Solution Approach 2:
The patent creates a multimode combustion system that can operate in both SI and LTC modes, making the engine universally adaptable to different operating conditions and expanding the overall operation range beyond what single-mode systems can achieve
4Power
If variable compression ratio is implemented to increase combustion thermal efficiency, then thermal efficiency improves, but pumping loss remains
Solution Approach 1:
The patent changes the valve timing parameters to create negative valve overlap, which actively compresses the air charge and raises in-cylinder pressure and temperature before combustion, thereby reducing pumping loss independently of compression ratio while maintaining high combustion thermal efficiency
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 enhances engine efficiency and reduces emissions by optimizing combustion processes at low loads, allowing for smoother transitions between operating modes and minimizing pumping losses.
Implementation Method 1
using an early exhaust valve closing (EVC) timing that creates an NVO during a gas exchange top dead center, to compress in-cylinder gas and increase overall gas temperature
Implementation Method 2
compress in-cylinder gas and increase overall gas temperature for improved fuel vaporization
Implementation Method 3
increase overall gas temperature for improved fuel vaporization
Implementation Method 4
using an early exhaust valve closing (EVC) timing that creates an NVO during a gas exchange top dead center, to compress in-cylinder gas and increase overall gas temperature
Data Source
AI summary
Systems and methods for improving engine low load performance are provided. The method may comprise performing a negative valve overlap (NVO) mode of operation, using an early exhaust valve closing (EVC) timing that is earlier than the intake valve opening timing and creates an NVO during a gas exchange top dead center, to compress in-cylinder gas and increase overall gas temperature for improved fuel vaporization, mixing, and reforming before the fuel-air mixture is burnt. With NVO operation, a low temperature combustion (LTC) mode may be used to improve engine combustion efficiency and reduce emissions. With the NVO operation at low loads, the engine intake may be wide open or less throttled, reducing pumping loss. A method based on a rate of change in the engine speed and load for the combustion mode transition between spark ignition (SI) and LTC modes is provided.