Variable Valve Timing Controller Low Voltage Current Limiting

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Solution Overview

Problem

Variable valve timing controllers with electric motors face failures due to decreased supply voltage, which can cause overheating and malfunction of switching elements in the motor drive circuit.

Innovation Solution

A variable valve timing controller that includes a target motor speed calculating means, a motor drive circuit with voltage detecting and current limiting capabilities to restrict output current when supply voltage falls below a certain threshold, preventing overheating and failure of switching elements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the supply voltage to the motor drive circuit decreases, then the motor operation becomes unstable, but restricting output current to prevent switching element failure causes slow response in valve timing control

Engineering Contradiction:

Improveswitching element reliabilityVSAvoidvalve timing control response speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The control device changes the operating parameters of the motor drive circuit by detecting supply voltage levels and dynamically adjusting the output current limits. When supply voltage drops below a predetermined threshold, the control device restricts the maximum output current to prevent switching element overheating, while still allowing the motor to operate at reduced capacity. This parameter adaptation resolves the contradiction by maintaining reliability under low-voltage conditions while accepting reduced performance.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the duty ratio of switching element is increased to control motor speed, then motor control precision improves, but switching element heat generation increases causing malfunction

Engineering Contradiction:

Improvemotor speed control precisionVSAvoidswitching element temperature

Core Design Contradiction:

Measurement precisionVSTemperature

Solution Approach 1:

The control device implements feedback control by continuously monitoring the supply voltage level and adjusting the output current limits accordingly. When supply voltage decreases, the feedback mechanism reduces the maximum duty ratio allowed for the switching elements, preventing excessive heat generation while maintaining adequate motor control precision through adaptive current limiting rather than relying solely on high duty ratios.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Instead of allowing full output current under all conditions, the control device applies partial action by restricting the maximum output current when supply voltage is low. This prevents the excessive action of over-driving the motor with insufficient voltage, which would cause switching element failure, while still providing sufficient current for basic motor operation and valve timing control.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If output current is restricted to prevent switching element failure, then reliability improves, but valve timing control response becomes slow

Engineering Contradiction:

Improvemotor drive circuit reliabilityVSAvoidvalve timing control speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The control device applies dynamic current limiting rather than static restriction. The output current limit is dynamically adjusted based on real-time supply voltage detection. When supply voltage is adequate, full current is allowed for rapid valve timing adjustments. When supply voltage drops, the current limit is dynamically reduced to prevent switching element failure. This dynamic adaptation resolves the contradiction by maintaining high productivity when possible while ensuring reliability when necessary.

Inventive Principle:

Principle #15Dynamics

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

The controller effectively prevents switching element failure by restricting output current and reducing heat generation when supply voltage drops, ensuring reliable operation and maintaining slow but stable valve timing control.

Implementation Method 1

a voltage detecting means for detecting a supply voltage supplied to the motor drive circuit

Methodology Applied

Scientific EffectVoltage detection: Ohm's Law

Implementation Method 2

a motor drive circuit which controls the driving current of the motor

Methodology Applied

Scientific EffectElectromagnetic conversion: Electromagnetic Induction

Implementation Method 3

there is a possibility that the switching elements generate heat to cause a malfunction thereof

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS7599782B2Variable valve timing controller for internal combustion engine

Publication Date: 2009.10.06 DENSO CORP

AI summary

An ECU outputs a signal indicative of a target motor speed calculated based on a deviation between a target camshaft phase and an actual camshaft phase to an EDU. The EDU performs a feedback control of the output current (motor current) of the EDU so that the deviation is decreased, whereby an actual camshaft phase is feedbacked to a target camshaft phase. When the supply voltage of EDU is less than the operation limit voltage established higher than minimum operation assurance voltage, the variation of the target motor speed is restricted. Thereby, the output current of EDU is restricted, and further, when the supply voltage is less than minimum operation assurance voltage, the output current of EDU is intercepted.