Internal Combustion Engine Load Control via Variable Valve Timing
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Solution Overview
Problem
Variable valve drive systems in internal combustion engines face challenges in low-load range operation, including precision issues with valve control and inaccurate air mass determination due to the need for short valve opening times and the limitations of air mass sensors designed for maximum-load conditions.
Innovation Solution
Implementing a method that uses a throttle flap for load regulation, with a predefined valve timing above a defined load threshold and a fixed valve timing below it, allowing the inlet valve to remain open longer and enabling accurate air mass estimation through volumetric efficiency characteristic maps, and incorporating a pilot-control value to adapt valve timings for rapid load changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a variable valve drive system is used to reduce fuel consumption and control engine load, then engine efficiency is improved, but valve control precision deteriorates in the low-load range due to the need for short valve opening times
Solution Approach 1:
The patent changes the operating parameters of the valve drive system by switching between two distinct valve timing strategies: above the load threshold, variable valve timing is used for optimization, while below the threshold, fixed valve timing with extended opening duration is applied. This parameter change resolves the contradiction by avoiding short valve opening times in low-load conditions, thereby maintaining valve control precision while preserving fuel efficiency benefits.
Solution Approach 2:
The system dynamically adapts its control strategy based on the current load condition. A regulator continuously monitors the load and switches between variable and fixed valve timing modes accordingly. This dynamic adaptation allows the system to maintain optimal performance across different operating ranges, preventing precision loss in low-load conditions while preserving energy efficiency improvements.
2Power
If variable valve timing is used to regulate engine load, then engine power control is improved, but air mass determination accuracy deteriorates in the low-load range due to low air mass flows
Solution Approach 1:
The patent introduces a volumetric efficiency characteristic map as an intermediary tool to determine air mass. Instead of relying solely on air mass sensors that fail at low flows, the system uses the characteristic map (which relates valve timing, engine speed, and volumetric efficiency) to calculate air mass indirectly. This intermediary approach maintains accurate air mass determination across the entire load range, including low-load conditions where direct sensing fails.
Solution Approach 2:
The patent replaces the mechanical/physical air mass sensing system with a computational approach using volumetric efficiency maps. By substituting direct measurement with calculation based on known engine parameters and characteristic data, the system overcomes the limitations of air mass sensors in low-flow conditions while maintaining accurate air mass determination for power control.
3Ease of operation
If the throttle flap is used for load regulation below the load threshold with fixed valve timing, then valve control handling is simplified, but rotational speed fluctuations increase during load changes
Solution Approach 1:
The system applies preliminary action by pre-defining optimal fixed valve timing values that are stored in advance. When the engine operates below the load threshold, these pre-determined timing values are immediately applied, eliminating the need for real-time calculation and complex control adjustments. This preliminary preparation simplifies valve control handling while the careful selection of these fixed values minimizes rotational speed fluctuations during load transitions.
Data Source
AI summary
A method and an arrangement for operating an internal combustion engine. According to the method, a load threshold is defined below which load control by a throttle valve is performed.