Variable Averaging Filter for Skip Fire Engine Control
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Solution Overview
Problem
Conventional filtering techniques are inadequate for handling the high-frequency variations in engine speed and intake air measurements during skip fire engine operation, leading to incomplete filtering and phase lag issues that affect engine control algorithms.
Innovation Solution
A variable averaging filter is employed, where the averaging period varies with the current operational firing fraction, using a tapped delay line or finite impulse response (FIR) filter to maximize attenuation at the fundamental frequency associated with the firing sequence, effectively filtering out oscillations at lower frequencies common in skip fire operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a simple low pass filter is used during skip fire operation, then the filtering of high frequency variations is achieved, but the phase lag and incomplete filtering at lower frequencies occur
Solution Approach 1:
The filter is designed with dynamic characteristics that adapt to the skip fire operating conditions. The filter coefficients are optimized to provide appropriate attenuation at the specific lower frequencies caused by skip fire operation while maintaining minimal phase lag, making the filter response dynamic rather than static
Solution Approach 2:
The filtering approach changes the parameters of the filter to specifically target the frequency characteristics of skip fire operation. By adjusting filter parameters to match the lower frequencies associated with reduced firing events, the system achieves effective filtering without the phase lag problems of conventional filters
2Ease of manufacture
If conventional filtering techniques are applied, then the implementation is simple, but the oscillatory behavior and phase lag affect control algorithms
Solution Approach 1:
The filter incorporates dynamic response characteristics that reduce oscillatory behavior while maintaining implementation feasibility. The optimized filter design provides reliable control signals without requiring complex hardware changes, balancing simplicity with improved control algorithm performance
3Use of energy by moving object
If the engine operates in skip fire mode, then the fuel efficiency is improved, but the engine speed and air intake measurements vary more significantly at lower frequencies
Solution Approach 1:
The filter parameters are specifically adjusted to match the lower frequency variations caused by skip fire operation. By changing the filter characteristics to align with the reduced firing frequency, the system maintains measurement stability while allowing the engine to operate in the fuel-efficient skip fire mode
Data Source
AI summary
A variety of methods, devices and filters are described that are suitable for averaging measured power train operating parameters over a period that varies as a function of an engine cylinder firing characteristic such as a current operational firing fraction or firing sequence. The averaged measured operating parameter may be used in a variety of different engine control related functions, calculations and/or operations. The described techniques and devices are particularly well suited for use during skip fire operation of an engine.