Variable Valve Timing Motor Current Restriction

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Solution Overview

Problem

Variable valve timing controllers with electric motors face issues with excessive motor coil temperature rise due to increased driving current, leading to durability deterioration and malfunction if not properly managed.

Innovation Solution

A variable valve timing controller that includes a target motor speed computing means, motor drive control means for feedback controlling motor current, and a motor current restricting means to limit the current when it exceeds an upper limit value, preventing excessive heat generation and temperature rise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If motor current is increased to improve valve timing control performance, then the responsiveness and accuracy of valve timing adjustment is improved, but the motor coil temperature rises excessively causing durability deterioration and malfunction

Engineering Contradiction:

Improvevalve timing control reliabilityVSAvoidmotor coil temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The control device uses periodic duty cycle control of the motor drive current based on elapsed time from the start of valve timing variation. By adjusting the duty cycle periodically rather than maintaining constant high current, the system achieves effective valve timing control while allowing the motor coil to cool between pulses, preventing excessive temperature rise and durability deterioration.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The control device dynamically adjusts the duty cycle of motor current based on the elapsed time from the start of valve timing variation. The duty cycle is set to a first value initially and changed to a second value (smaller than the first) after a predetermined time elapses. This dynamic adjustment optimizes control effectiveness early in the variation process while preventing overheating as the operation continues.

Inventive Principle:

Principle #15Dynamics

2Measurement precision

If feedback control is continuously applied to reduce deviation between target and actual motor speed, then the valve timing accuracy is improved, but the motor current increases and coil temperature exceeds allowable limits

Engineering Contradiction:

Improvevalve timing accuracyVSAvoidmotor coil heat generation

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

Instead of continuous high-level feedback control that generates excessive heat, the system applies feedback control with periodic duty cycle adjustment. The duty cycle is reduced after a predetermined time elapses, which maintains sufficient valve timing accuracy while significantly reducing the harmful heat generation in the motor coil.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The control device applies partial feedback control action by reducing the duty cycle after a predetermined time. This partial action (using a smaller duty cycle value) is sufficient to maintain acceptable valve timing accuracy while avoiding the excessive heat generation that would result from continuous full-strength feedback control.

Inventive Principle:

Principle #16Partial or excessive 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

Effectively restricts motor current to prevent coil temperature from exceeding safe limits, thereby preventing durability deterioration and malfunction, ensuring continuous operation within heat generation limits.

Implementation Method 1

an electric motor as a driving source. A rotation speed of the electric motor is varied to adjust a rotational phase of the camshaft relative to a crankshaft

Methodology Applied

Scientific EffectElectromagnetic interaction: Electromagnetic Induction

Implementation Method 2

as a driving current of the motor (motor current) increases during the variable valve timing control, the heat value of the motor increases and a coil temperature rises

Methodology Applied

Scientific EffectResistive heating: Joule Heating

Data Source

PatentUS7584729B2Variable valve timing controller for internal combustion engine

Publication Date: 2009.09.08 DENSO CORP

AI summary

A motor current (driving current of motor) is estimated based on a target motor speed, an actual motor speed, and an engine speed. When the estimated motor current exceeds the upper limit value equivalent to a heat generation limiting current, the motor current is restricted by restricting a variation (motor speed F/B amount) in target motor speed outputted to an EDU from an ECU. If it is continued that a deviation between the target motor speed and the actual motor speed exceeds a predetermined value, the estimated motor current exceeds this upper limit value and the restricting action of the motor current is continued.