Variable Camshaft Timing Control via Position Estimation
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Solution Overview
Problem
Existing variable camshaft timing systems face challenges in effectively controlling camshaft timing due to low sampling rates, particularly at low engine speeds or during rapid engine speed changes, leading to inadequate response times and performance during transient operating conditions.
Innovation Solution
The system adjusts the camshaft phaser using a camshaft duty cycle signal based on both sampled and estimated camshaft positions, with the estimated position calculated via a model of the VCT system, allowing for higher frequency control and improved response times across a range of engine conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the camshaft position is sampled based on the rotation of the camshaft trigger wheel edge passing a camshaft position sensor, then the sampling method is simple and reliable, but the sampling rate becomes too low at low engine speeds or during rapid engine speed changes, leading to insufficient control response
Solution Approach 1:
The patent introduces an intermediary estimator that processes the discrete sampled camshaft position data to generate continuous position information. The estimator acts as a mediator between the sampled position signals and the VCT control system, converting discrete samples into continuous control-ready signals through mathematical estimation, thereby enabling high-rate control without increasing the physical sampling rate
Solution Approach 2:
The patent replaces the mechanical sampling approach (relying on physical trigger wheel edges passing a sensor) with a computational estimation approach. Instead of increasing mechanical sampling frequency, the system uses software-based estimation algorithms to generate high-frequency position information from low-frequency physical samples, substituting mechanical limitations with computational solutions
2Device complexity
If the camshaft position sampling period is determined by engine speed and number of trigger wheel edges, then the system structure is simple, but the response time becomes too long during transient operating conditions, failing to meet dynamic control requirements
Solution Approach 1:
The patent performs preliminary estimation of camshaft position between actual samples using the known duty cycle signal and VCT system model. By predicting intermediate position values in advance, the system prepares control data ahead of time, reducing the effective response time without requiring faster physical sampling or more complex hardware structures
Solution Approach 2:
The patent creates a computational copy of the camshaft position information through estimation algorithms. Instead of relying on direct physical measurements only, the system generates estimated position copies that fill in the gaps between actual samples, enabling continuous control based on replicated position data rather than waiting for next physical sample
3Stability of the object's composition
If the camshaft duty cycle is controlled at low frequency to match the sampling rate, then the control system is stable and simple, but the VCT system cannot respond adequately to dynamic changes in engine operating conditions
Solution Approach 1:
The patent makes the control system dynamic by continuously updating the estimated camshaft position between samples based on the duty cycle signal and system model. This dynamic estimation process allows the control system to adapt to changing engine conditions in real-time, transforming a static low-frequency control approach into a dynamic high-frequency responsive system while maintaining simplicity
Data Source
AI summary
Methods and systems are provided for controlling a variable camshaft timing system. In one example, a method may include actuating a camshaft phaser with a camshaft duty cycle determined based on a sampled camshaft position and an estimated camshaft position, the estimated camshaft position determined based on a previously determined camshaft duty cycle.