Semiconductor Switch Protection Circuit for Electric Motor Steering

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Solution Overview

Problem

Electromechanical motor vehicle power steering systems face issues with semiconductor switch damage due to overvoltages when switching off, as the voltage at the semiconductor switch can exceed its maximum reverse voltage during current interruption, leading to potential failure and unsafe steering resistance.

Innovation Solution

Incorporating a protective device with suppressor diodes connected in parallel to the safety switches and Schottky diodes in series with them, which conduct overvoltages past the safety switches, preventing damage by redirecting excessive current and ensuring the system's safety during switching processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the semiconductor switch is opened to interrupt current flow, then the steering assistance can be deactivated, but overvoltage occurs at the semiconductor switch which can exceed its maximum reverse voltage and cause damage

Engineering Contradiction:

Improvesafety of steering systemVSAvoidovervoltage damage to semiconductor switch

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A protective device is introduced as an intermediary element between the semiconductor switch and the circuit. This protective device includes a first diode connected in parallel with the semiconductor switch and a second diode connected in series with the first diode, forming a protective circuit path that diverts overvoltage away from the semiconductor switch.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The protective device utilizes the harmful overvoltage energy by providing an alternative current path through the diodes. When overvoltage occurs, the diodes conduct the excess current in a controlled manner, converting the potentially damaging overvoltage into a beneficial protective mechanism that safeguards the semiconductor switch.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Ease of operation

If the current flow is interrupted by the semiconductor switch, then the steering assistance can be stopped, but the voltage at the semiconductor switch rises to a value higher than the supply voltage

Engineering Contradiction:

Improvecontrol of steering assistanceVSAvoidvoltage stress on semiconductor switch

Core Design Contradiction:

Ease of operationVSStress or pressure

Solution Approach 1:

The protective device with the diode configuration is pre-installed in parallel with the semiconductor switch before any overvoltage event occurs. This protective circuit acts as a cushion or buffer that is already in place to absorb and redirect voltage spikes, preventing them from reaching damaging levels at the semiconductor switch.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Strength

If an excessively high flow of current through the semiconductor switch during switching off is avoided, then the semiconductor switch is protected, but the steering assistance cannot be quickly deactivated in fault conditions

Engineering Contradiction:

Improveprotection of semiconductor switchVSAvoidresponse time for fault deactivation

Core Design Contradiction:

StrengthVSSpeed

Solution Approach 1:

The protective device dynamically responds to voltage conditions. During normal operation, the diodes remain non-conductive and do not interfere with semiconductor switch operation. When overvoltage occurs during switching off, the diodes automatically become conductive, providing a dynamic current path that protects the semiconductor switch without affecting normal switching performance.

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 solution effectively protects semiconductor switches from damage by managing overvoltages and preventing induction current short-circuits, ensuring the reliability and safety of the electromechanical power steering system.

Implementation Method 1

The protective device (25) comprises in each case at least one suppressor diode (28) which is connected in parallel with the respective safety switch (19, 20, 21) and arranged in the forward conducting direction with respect to the onboard DC power supply

Methodology Applied

Scientific EffectDiode effect: Diode

Implementation Method 2

each safety switch (19, 20, 21) having a body diode (17) in the forward conducting direction with respect to the onboard DC power supply

Methodology Applied

Scientific EffectDiode forward conduction: Diode

Data Source

PatentUS11381194B2Protective device for a semiconductor switch of an electric motor of an electromechanical motor vehicle steering system

Publication Date: 2022.07.05 THYSSENKRUPP PRESTA AG

AI summary

An electromechanical motor vehicle power steering system having a multiphase, permanently excited electric motor via a controller and supply lines from an onboard power supply of a motor vehicle.