CVVT Cam Undershoot Compensation via Ignition Timing
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Solution Overview
Problem
The intermediate lock position continuously variable valve timing system experiences a drop in engine RPM due to cam undershoot, leading to instability during engine starting, which is challenging to address without physical limitations in the response speed of the valve plunger.
Innovation Solution
A method involving the engine Electronic Control Unit (ECU) to determine the cam position and compensate the ignition timing to prevent cam undershoot by adding a CVVT compensation ignition timing to the current ignition timing, thereby preventing engine RPM drops without altering the hardware structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ECU moves the parking position to an advanced position during engine starting, then the valve timing is optimized for starting, but the cam may undershoot to a retarded position causing RPM drop
Solution Approach 1:
The ignition timing is compensated in advance before the cam position control is executed. The ECU calculates the required ignition timing compensation based on the target cam position and applies it proactively, preventing the RPM drop that would occur if the cam undershoots to a retarded position during the transition to the advanced parking position.
Solution Approach 2:
The invention changes the ignition timing parameter dynamically based on the cam position and operating conditions. By adjusting the ignition timing compensation value according to the specific situation (engine speed, load, temperature), the system optimizes the balance between achieving the target cam position and preventing RPM drop during the transition.
2Manufacturing precision
If the plunger response speed is increased to prevent cam undershoot, then the cam position control is improved, but there is a physical limit to how fast the plunger can move
Solution Approach 1:
The invention replaces the mechanical approach of increasing plunger response speed with a control system approach. Instead of modifying the mechanical components (plunger, solenoid valve) to move faster, the system uses electronic control to compensate for the inherent mechanical delays by adjusting the ignition timing, thereby achieving the same goal without hardware changes.
Solution Approach 2:
The ignition timing compensation acts as an intermediary mechanism between the cam position control system and the engine output. Rather than directly trying to make the plunger respond faster, the system uses ignition timing adjustment as a mediating variable to compensate for the plunger's response delay and prevent cam undershoot.
3Reliability
If ignition timing compensation is applied to prevent cam undershoot, then RPM stability is maintained, but the ignition timing control complexity increases
Solution Approach 1:
The ignition timing compensation is determined based on feedback from the actual cam position and operating conditions. The ECU continuously monitors the cam position and adjusts the ignition timing compensation accordingly, creating a closed-loop control system that maintains RPM stability while adapting to changing conditions without requiring complex additional hardware.
Data Source
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AI summary
A method for improving performance of a system that controls a intermediate lock position continuously variable valve may include: obtaining a cam position using an engine Electronic Control Unit (ECU) that has started controlling a position of a intermediate lock position Continuously Variable Valve Timing System (CVVT); determining, using the ECU, whether the cam position corresponds to parking of the intermediate lock position CVVT; compensating an engine ignition timing to prevent cam undershoot, if it is determined that the cam position corresponds to the parking of the intermediate lock position CVVT; and returning to ignition timing control according to an engine operation condition after compensating the engine ignition timing.