Feed Forward Dynamic Spool Valve for Cam Timing Control
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Solution Overview
Problem
Existing variable cam timing (VCT) systems face challenges in accurately controlling cam position at high engine RPM, leading to unintended oil drainage and cam oscillations, which result in engine knocking and degradation due to insufficient control systems and oil leakage.
Innovation Solution
A solenoid-controlled spool valve is used to modulate oil flow in the hydraulic VCT system, maintaining oil volume and cam timing by blocking unintended oil flow through the null position, synchronized with engine firing frequency to counteract cam torque oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional spool valve control system is used at high engine RPM, then the system structure remains simple, but cam timing control accuracy deteriorates due to insufficient control during cam torque oscillation events
Solution Approach 1:
The patent applies periodic action by modulating the spool valve with a component at engine firing frequency to counteract cam torque oscillations. The controller modulates the spool valve position periodically at the same frequency as the cam torque oscillations, creating a feedforward control signal that proactively compensates for timing deviations before they occur, thereby improving cam timing control accuracy at high RPM without requiring complex additional hardware
Solution Approach 2:
The patent implements feedback control by using cam position sensors to detect actual cam timing and comparing it with desired timing, then using this error signal to adjust spool valve positioning. This feedback mechanism continuously corrects cam timing deviations caused by oil pressure variations and torque oscillations, maintaining accurate control despite the simplicity of the underlying spool valve structure
2Stability of the object's composition
If the spool valve is held at null position to maintain current cam timing, then cam timing stability is improved, but oil drainage increases due to unintended oil flow during cam torque oscillations
Solution Approach 1:
The patent applies preliminary action by predicting and counteracting cam torque oscillations before they cause significant oil drainage. The controller generates a feedforward modulation signal at engine firing frequency that proactively adjusts spool valve positioning to prevent unintended oil flow during torque oscillation events, thereby maintaining cam timing stability while minimizing oil loss before it occurs
Solution Approach 2:
The patent implements preliminary anti-action by applying a counteracting force through spool valve modulation that opposes the anticipated cam torque oscillations. The controller deliberately introduces a counter-oscillation signal that opposes the natural torque oscillations, preventing the conditions that would lead to excessive oil drainage while maintaining timing stability
3Ease of manufacture
If conventional feedback control is used without feedforward modulation, then the control system is easier to implement, but cam oscillations increase leading to engine knocking and part degradation
Solution Approach 1:
The patent applies periodic action by modulating the spool valve with a component at engine firing frequency to counteract cam torque oscillations. The controller modulates the spool valve position periodically at the same frequency as the cam torque oscillations, creating a feedforward control signal that proactively compensates for timing deviations before they occur, thereby improving cam timing control accuracy at high RPM without requiring complex additional hardware
Solution Approach 2:
The patent implements feedback control by using cam position sensors to detect actual cam timing and comparing it with desired timing, then using this error signal to adjust spool valve positioning. This feedback mechanism continuously corrects cam timing deviations caused by oil pressure variations and torque oscillations, maintaining accurate control despite the simplicity of the underlying spool valve structure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach stabilizes the hydraulic system, maintaining consistent combustion performance across engine cylinders by counteracting cam torque effects, even under time-varying disturbance torques, thereby reducing engine knocking and part degradation.
Implementation Method 1
The performance of this device is thus dependent on oil pressure, which can be a function of engine speed and leakage through various oil systems
Implementation Method 2
actuating a spool valve via a solenoid to advance and retard a hydraulic variable cam timing actuator
Implementation Method 3
the solenoid modulation enables the spool valve to block the flow of oil that may otherwise occur due to the force on the camshaft by the actuation of the cylinder valves
Implementation Method 4
modulating the solenoid with a component at a frequency synchronous to engine firing frequency to counteract cam torque oscillations
Data Source
AI summary
A method of controlling a spool valve through feedback and feedforward mechanisms is described. In one example, a method includes actuating a spool valve via a solenoid to advance and retard a hydraulic variable cam timing actuator coupled to a camshaft, and while commanded to a null position to maintain current cam timing, modulating the solenoid with a component at a frequency synchronous to engine firing frequency to counteract cam torque oscillations. In this way, a spool valve may be maintained in a null position despite high cam torque oscillation frequency, thereby retaining oil in a solenoid assembly and improving can timing position.