Variable Valve Lift and Skip Fire Engine Control
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Solution Overview
Problem
Conventional internal combustion engines face challenges in achieving optimal fuel efficiency and minimizing pumping losses, particularly at low engine loads, due to limitations in variable valve lift control and skip fire operations, which often result in increased pumping losses and undesirable noise, vibration, and harshness (NVH) characteristics.
Innovation Solution
Implementing a combination of cylinder deactivation and variable valve lift control, where at least one cylinder bank is capable of deactivation and another bank is controlled using variable valve lift, allowing for precise regulation of air intake and eliminating the need for a throttle, thereby reducing pumping losses and enhancing fuel efficiency while maintaining desirable NVH characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If variable valve lift control is used to adjust mass air charge, then fuel efficiency is improved by reducing pumping losses, but hardware cost and control complexity increase
Solution Approach 1:
The engine is divided into two separate cylinder banks, each with independent control capabilities. Bank 1 is equipped with variable valve lift control for precise air charge regulation, while Bank 2 is equipped with skip fire capability for selective cylinder deactivation. This segmentation allows each bank to operate independently, providing flexible control over the entire engine's output while maintaining simpler individual control systems for each bank.
Solution Approach 2:
The system dynamically switches between different operational modes depending on engine load conditions. At low loads, Bank 2 cylinders are deactivated via skip fire control while Bank 1 provides baseline power with variable valve lift optimization. At intermediate loads, variable valve lift on Bank 1 cylinders is adjusted to match torque requirements. This dynamic operation allows the engine to adapt to varying power demands while maintaining optimal efficiency across different operating points.
2Use of energy by moving object
If skip fire control is used to vary cylinder torque output, then fuel efficiency is improved, but noise, vibration, and harshness characteristics deteriorate
Solution Approach 1:
By segmenting the engine into two independently controllable banks, the system can use skip fire control on Bank 2 while Bank 1 continues to operate all cylinders smoothly. This segmentation distributes the torque delivery across different cylinder groups, helping to smooth out vibrations and reduce NVH issues that would occur if skip fire were applied to all cylinders simultaneously.
Solution Approach 2:
The system changes operational parameters dynamically based on load conditions. At low loads where skip fire is most beneficial for efficiency, Bank 1 maintains full cylinder operation with optimized valve lift to provide smooth torque delivery. As load increases and all Bank 2 cylinders are reactivated, variable valve lift timing and duration are adjusted to optimize combustion characteristics and minimize vibrations, thereby improving NVH characteristics across the operating range.
3Ease of operation
If throttle position is adjusted to control mass air charge, then air/fuel ratio control is simplified, but pumping losses increase reducing fuel efficiency
Solution Approach 1:
The system extracts the air charge control function from the throttle and relocates it to the variable valve lift mechanism on Bank 1. By closing the intake valves early in the intake stroke, the system effectively removes air from entering the cylinder without requiring throttle restriction. This extraction of the throttling function eliminates the associated pumping losses while maintaining simple stoichiometric fuel injection control.
Solution Approach 2:
The mechanical throttle system is replaced with a valve timing control system on Bank 1. Instead of using a mechanical throttle blade to restrict airflow, the system uses electronically controlled variable valve lift mechanisms to regulate air charge by controlling valve opening duration and timing. This substitution eliminates the mechanical throttling process and its associated energy losses while maintaining precise air/fuel ratio control through electronic management.
Data Source
AI summary
An internal combustion engine capable of cylinder deactivation or skip fire control in combination with variable valve lift control. One bank of cylinders can be deactivated while the air induction of the other bank of cylinders is regulated using variable valve lift control to increase engine efficiency. An internal combustion engine with two cylinder banks, where control of one cylinder bank using skip fire control can be operating at an appropriate firing fraction in combination with variable valve lift control on the other cylinder bank. A single bank of cylinders can be controlled in a skip fire manner in conjunction with variable valve lift control.