Crank Encoder Signal Discrimination via Period Validation
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Solution Overview
Problem
Internal combustion engines face synchronization issues due to spurious electrical noise spikes in crankshaft rotary position encoder signals, leading to misfiring and incorrect spark and fuel delivery.
Innovation Solution
An engine controller is programmed to trigger an interrupt service routine on every edge of the encoder signal, calculating and storing periods to determine engine acceleration or deceleration, and only recognizes signals within a predicted time window based on realistic limits, rejecting signals outside this window as spurious.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine controller uses a toothed wheel encoder to generate timing signals, then the spark and fuel injection timing can be controlled, but electrical noise spikes may be interpreted as valid signals causing misfiring and incorrect timing
Solution Approach 1:
The system performs preliminary calculations of expected signal periods and acceleration limits before noise interference occurs. By pre-establishing the timing window based on realistic engine acceleration limits, the controller can preemptively reject spurious signals before they cause misfiring or timing errors.
Solution Approach 2:
The system continuously monitors actual encoder signal periods and compares them against calculated expected periods based on current engine speed and acceleration. This feedback mechanism allows the controller to detect and reject noise spikes by identifying periods that fall outside the expected range, while maintaining accurate timing control.
2Measurement precision
If the controller counts all encoder teeth signals, then the rotational position can be determined, but spurious signals cause the controller to count incorrect number of teeth leading to loss of synchronization
Solution Approach 1:
The system changes the parameter used for signal validation from simple edge detection to period-based validation. By calculating the period of each encoder signal and comparing it against expected values derived from engine acceleration limits, the system can distinguish between valid teeth signals and spurious noise, maintaining accurate rotational position measurement while rejecting false signals.
3Productivity
If the system accepts all encoder signals without validation, then the response time is fast, but misfiring and incorrect spark delivery occur due to noise spikes
Solution Approach 1:
The system applies partial validation by checking only the critical period parameter of each signal rather than performing comprehensive analysis. This partial action approach maintains fast response by validating only the essential timing information needed to distinguish valid signals from noise, while sufficient to prevent misfiring and ensure accurate spark delivery.
Data Source
AI summary
A system for discrimination of spurious crankshaft encoder signals. A position encoder connected to an engine crankshaft sends a pulsed signal indicative of crankshaft rotational performance to an engine controller. The controller is programmed to trigger an interrupt service routine (ISR) on every falling or rising edge of each pulse. The ISR calculates and stores the period of each pulse and the period of the previous pulse and calculates the rotational speed and instantaneous acceleration or deceleration of the engine at all times. The controller is further programmed with realistic engine acceleration and deceleration limits and recognizes a next signal only within a time window corresponding to those limits and the engine speed. Signals arriving outside the calculated time window are considered spurious and are rejected. The system improves engine performance by preventing loss of synchronization between spark and fuel injection and piston and valve timing.