Electric VCT Actuator Camshaft Position Control

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Solution Overview

Problem

Electric Variable Cam Timing (VCT) systems face challenges in maintaining the camshaft position during engine shutdown and startup due to lack of locking pins, leading to camshaft drift caused by friction drag, especially when closed-loop feedback is unavailable at low engine speeds.

Innovation Solution

Applying specific current levels to the electric VCT actuator during engine shutdown and startup to maintain the camshaft at a target position, with adjustable currents based on conditions to counteract valvetrain torque, ensuring the camshaft remains at the desired position until feedback control is regained.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the VCT system moves the camshaft to the desired position before engine shut-down, then the camshaft is positioned correctly for the first firing event, but the camshaft drifts to a retarded position during uncontrolled phases due to friction drag effects

Engineering Contradiction:

Improvecamshaft position accuracyVSAvoidcamshaft position maintenance

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The system performs preliminary positioning of the camshaft to the desired location before engine shut-down occurs. This preliminary action ensures the camshaft is in the correct position for the first firing event, and the patent applies holding currents during the uncontrolled phases to maintain this position against friction drag effects.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system applies preliminary anti-action by using holding currents to counteract the friction drag effects that would otherwise cause the camshaft to drift to a retarded position during the uncontrolled phases when closed-loop feedback is unavailable.

Inventive Principle:

Principle #9Preliminary anti-action

2Reliability

If locking pins are added to keep the camshaft in the desired position, then camshaft position stability is improved, but device complexity increases

Engineering Contradiction:

Improvecamshaft position stabilityVSAvoidVCT system structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical locking pin system with an electrical solution. Instead of using mechanical components to physically lock the camshaft in position, the system uses electric currents applied to the VCT actuator to maintain the camshaft at the desired position during uncontrolled phases, thereby reducing mechanical complexity while achieving the same stability goal.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Manufacturing precision

If closed-loop feedback control is used to position the camshaft, then positioning accuracy is improved, but control is unavailable when engine speed drops below threshold during shut-down and start-up

Engineering Contradiction:

Improvecamshaft positioning accuracyVSAvoidcontrol availability

Core Design Contradiction:

Manufacturing precisionVSEase of operation

Solution Approach 1:

The system uses holding currents as an intermediary control mechanism during the transition phases when closed-loop feedback is unavailable. These currents act as a mediator to maintain camshaft position stability during engine shut-down and start-up when engine speed is below the threshold for reliable feedback, bridging the gap between available and unavailable control states.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If the VCT actuator is powered continuously to maintain camshaft position, then position stability is improved, but energy consumption increases

Engineering Contradiction:

Improvecamshaft position maintenanceVSAvoidVCT actuator power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The system applies periodic action by using holding currents only during specific uncontrolled phases when closed-loop feedback is unavailable (engine shut-down and start-up below threshold). The VCT actuator is not continuously powered but receives targeted current applications only when needed to maintain position during these transient uncontrolled periods, reducing overall energy consumption while maintaining stability when required.

Inventive Principle:

Principle #19Periodic action

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

Prevents camshaft drift from the target position during uncontrolled phases, reducing the time to achieve the target position when feedback control is restored, and ensuring accurate camshaft positioning for the first firing event.

Implementation Method 1

Applying specific current levels to the electric VCT actuator during engine shutdown and startup to maintain the camshaft at a target position

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Implementation Method 2

the position of the camshaft may be moved to a retarded position due to friction drag effects during the un-controlled phases

Methodology Applied

Scientific EffectFriction drag: Friction

Data Source

PatentUS9243569B2Variable cam timing control during engine shut-down and start-up

Publication Date: 2016.01.26 FORD GLOBAL TECH LLC

AI summary

A method for controlling an electric variable cam timing (VCT) actuator is disclosed. The method includes during engine shutdown, adjusting camshaft position with an electric VCT actuator to a target starting location, applying a first current to the electric VCT actuator to maintain the target starting location, and during engine startup before camshaft position feedback becomes available, applying a second current to the electric VCT actuator to maintain the target starting location.