Electric Drive Speed Limiting From Supply Line Thermal Load

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Solution Overview

Problem

Existing temperature protection methods for electric drive devices focus on evaluating phase currents or motor winding currents, failing to account for the thermal status of other components in the supply line, leading to incomplete thermal overload prevention.

Innovation Solution

The method involves ascertaining the current strength through the supply line and adjusting the maximum rotor shaft target speed based on permissible temperature loads, using current sensors and thermal models to ensure accurate and robust thermal management.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If phase current or motor winding current is evaluated for thermal protection, then motor thermal overload is prevented, but thermal overload of other supply line components is not prevented

Engineering Contradiction:

Improvethermal protection coverageVSAvoidthermal overload risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

Instead of measuring current at the motor terminals (phase current or winding current), the patent inverts the measurement approach by measuring the supply line current upstream. This allows monitoring of thermal load for all components in the supply line, not just the motor, thereby expanding thermal protection coverage to include other components that were previously unprotected.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The supply line current measurement serves multiple functions simultaneously: it monitors motor thermal load, monitors thermal load of supply line components, and provides a comprehensive thermal status indicator for the entire drive system. This multi-functional approach resolves the limitation of phase current measurement which only protects the motor.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If target speed is increased to temporarily idle the motor, then motor thermal overload is avoided, but supply line current is not reduced

Engineering Contradiction:

Improvethermal overload preventionVSAvoidsupply line current consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent implements feedback control by continuously monitoring supply line current and using this information to dynamically adjust the maximum target speed. When supply line current exceeds permissible limits, the system reduces the maximum target speed to reduce current consumption, creating a closed-loop control that simultaneously addresses thermal protection and energy consumption.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system changes the operational parameters by dynamically adjusting the maximum target speed based on thermal conditions and current measurements. This parameter adjustment allows the motor to operate at reduced speeds when thermal limits are approached, thereby reducing supply line current consumption while still providing thermal protection.

Inventive Principle:

Principle #35Parameter changes

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 effectively prevents thermal overload in all operating situations by demand-based reduction of target speed and supply line current, ensuring reliable thermal protection for the electric machine.

Implementation Method 1

a current strength of an electric current flowing through a supply line of the machine is ascertained

Methodology Applied

Scientific EffectElectrical current measurement: Ohm's Law

Implementation Method 2

a maximum value for a target speed of a rotor shaft of the machine is at least temporarily reduced according to the ascertained current strength and a permissible temperature load

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS20260031754A1Method for operating an electric drive device, electric drive device

Publication Date: 2026.01.29 ROBERT BOSCH GMBH

AI summary

A method for operating an electric drive device. The drive device includes an electric machine. A current strength of an electric current flowing through a supply line of the machine is ascertained, and a maximum value for a target speed of a rotor shaft of the machine is at least temporarily reduced according to the ascertained current strength and a permissible temperature load of at least one component of the electric machine. An electric drive device is also described having an electric machine. A current detection module ascertains a current strength of an electric current flowing through a supply line of the machine, and a maximum value definition module at least temporarily reduces a maximum value for a target speed of a rotor shaft of the machine according to the ascertained current strength and a permissible temperature load of at least one component of the electric machine.