Electric Power Assist Steering Torque Offset Calculation

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Solution Overview

Problem

Existing methods for transforming desired rack force injection to handwheel torque offset in electric power assist steering systems are imprecise, leading to inconsistent performance and safety concerns due to dependence on driving conditions.

Innovation Solution

A method is developed to determine a preferred handwheel torque offset by calculating a column torque offset as a function of both the driver-applied torque and the requested assist torque, using an inverse boost curve to accurately reflect driving conditions and ensure consistent performance of driving assist functionalities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If known techniques are used to transform desired rack force injection to handwheel torque offset, then the transformation can be performed, but the precision and accuracy are insufficient leading to noticeable differences between desired and implemented rack force injection

Engineering Contradiction:

Improvetransformation precisionVSAvoidperformance consistency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the transformation parameters by incorporating driver-applied torque as an additional parameter alongside desired rack force injection. This creates a more comprehensive transformation model that accounts for both the desired assist force and the actual driver input, thereby improving precision and reducing the noticeable differences between desired and implemented rack force injection.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback by using the actual driver-applied torque measurement to adjust and refine the handwheel torque offset calculation. This feedback loop ensures that the transformation accurately reflects real-time driving conditions, improving both precision and performance consistency across different driving scenarios.

Inventive Principle:

Principle #23Feedback

2Reliability

If rack output force limits are established for safety, then safety limits can be enforced, but the limits are less than desirable because they have considerable dependence on driving conditions

Engineering Contradiction:

Improvesafety limit enforcementVSAvoiddriving condition adaptability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent makes the safety limits dynamic by incorporating driving condition parameters into the transformation process. Instead of fixed rack output force limits, the system dynamically adjusts the handwheel torque offset based on actual driving conditions, allowing safety limits to adapt to curves, straight driving, and other scenarios while maintaining enforcement reliability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter set used for establishing safety limits by including driver-applied torque and desired rack force injection together in the transformation. This creates a more versatile safety enforcement mechanism that adapts to different driving conditions rather than relying on fixed limits that are less than desirable.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If dual torque injection is implemented to allow driver handwheel torque injection to be realized as rack force output, then the torque injection can be achieved, but the imprecise transformation creates noticeable differences between desired and implemented rack force

Engineering Contradiction:

Improvetorque injection implementationVSAvoidrack force injection accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent improves rack force injection accuracy by changing the transformation parameters to include both desired rack force injection and driver-applied torque. This enhanced parameter set enables dual torque injection to be implemented more precisely, reducing the noticeable differences between desired and implemented rack force while maintaining ease of operation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the imprecise mechanical transformation approach with a more accurate computational transformation that uses both desired rack force injection and driver-applied torque measurements. This substitution improves the accuracy of rack force injection implementation while maintaining the dual torque injection mechanism's ease of operation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS9352775B2Method for determining assist torque offset and system using same

Publication Date: 2016.05.31 FORD GLOBAL TECH LLC

AI summary

A vehicle having a driving assist system and an electric power assist steering system coupled to the driving assist system. The driving assist system transmits an assist torque request for reception by the electric power assist steering system for enabling the electric power assist steering system to adjust its outputted assist torque to accommodate requirements of the driving assist system. The assist torque request specifies a requested additional assist torque required by the driving assist system from the electric power assist steering system. In response to receiving the assist torque request, the electric power assist steering system performs an operation for determining a column torque offset as a function of both a force being applied by a driver of the vehicle on a steering column of the vehicle and the requested additional assist torque required by the driving assist system.