Modified Static Tire Model for Steering Rack Force Estimation

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Solution Overview

Problem

In electric power steering (EPS) systems, the inability of hand wheel torque sensors to function properly can lead to a loss of steering assist torque, especially at low vehicle speeds, resulting in inadequate steering assistance.

Innovation Solution

A method and system that estimate the steering rack force using a modified static tire model, allowing the control module to generate a steering assist torque command even when hand wheel torque sensors are disabled, by incorporating sensor data from other sources like hand wheel angle, velocity, and vehicle velocity, and adjusting for surface friction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If hand wheel torque sensors are used to determine driver requested assist torque, then steering assist torque can be provided, but the system becomes unreliable when the torque sensor malfunctions or is disabled

Engineering Contradiction:

Improvesteering assist torque reliabilityVSAvoidtorque sensor dependency

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary estimation system that uses alternative sensors (accelerometer, gyroscope, position sensors) to calculate steering rack force when the primary torque sensor is unavailable. This intermediary system acts as a mediator between the failed torque sensor and the power steering actuator, maintaining system functionality through indirect measurement and calculation of steering requirements.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the direct mechanical torque sensing system with an alternative measurement approach using inertial sensors (accelerometers and gyroscopes) combined with computational algorithms. This substitution transitions from direct mechanical torque measurement to indirect measurement through motion dynamics analysis, eliminating the single point of failure represented by the torque sensor.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If torque sensor failure is detected, then system safety is improved, but steering assist is lost at low vehicle speeds where it is most needed

Engineering Contradiction:

Improvesystem safetyVSAvoidsteering assistance availability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent implements beforehand cushioning by preparing an alternative torque estimation system that is ready to activate immediately upon torque sensor failure detection. The system pre-establishes the computational framework using available sensors (accelerometer, gyroscope, position sensors) so that when failure occurs, the transition to alternative estimation is seamless, cushioning against the loss of steering assist during critical low-speed maneuvers.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The patent changes the measurement parameters from direct torque sensing to indirect parameter estimation using acceleration, angular velocity, and position data. By transforming the problem from measuring torque directly to calculating it from motion parameters, the system maintains steering assist functionality through parameter substitution when the original measurement method fails.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a modified static tire model is used to estimate steering rack force, then steering assist is maintained without torque sensors, but the estimation complexity increases

Engineering Contradiction:

Improvesteering assist continuityVSAvoidestimation algorithm complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent creates a computational model (modified static tire model) that copies and simulates the physical tire-road interaction characteristics. Instead of directly measuring torque, the system uses the tire model to replicate the relationship between steering input and rack force based on available sensor data, providing a virtual copy of the torque information that would otherwise require a physical torque sensor.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent makes the alternative estimation system universal by designing it to work across various operating conditions using a combination of sensors (accelerometer, gyroscope, position sensors) and a flexible computational model. The system can adapt to different vehicle speeds, steering rates, and road conditions, providing reliable steering assist estimation through multi-functional sensor integration and model-based calculation.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS10144445B2Modified static tire model for providing assist without a torque sensor for zero to low vehicle speeds

Publication Date: 2018.12.04 STEERING SOLUTIONS IP HOLDING CORP

AI summary

A method of controlling an electric power steering system is provided. The method estimates steering rack force to be caused by a tire and a surface of a ground with which the tire is in contact in response to determining that one or more hand wheel torque sensors are not enabled. The method generates a steering assist torque command based on the estimated steering rack force. The method controls the electric power steering system using the steering assist torque command.