Electric Power Steering Assist Torque via Lateral Acceleration
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Solution Overview
Problem
Faulty hand wheel torque sensors in electric power steering systems can lead to inadequate assist torque provision and necessitate a vehicle to operate in a limited Limp Home mode, which is undesirable.
Innovation Solution
A method and system that estimate assist torque based on vehicle lateral acceleration or non-straight movement rate using hand wheel angle, allowing the electric power steering system to function even when hand wheel torque sensors are faulty, by employing a control module that generates assist torque commands and controls the steering system accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hand wheel torque sensors are used to determine driver requested assist torque, then the EPS system can provide accurate assist torque, but the system becomes vulnerable to sensor failures requiring Limp Home mode
Solution Approach 1:
The patent changes the parameter used for assist torque calculation from direct torque sensor signals to alternative parameters such as hand wheel angle, vehicle speed, and steering ratio. This parameter substitution allows the system to calculate assist torque without relying on faulty torque sensors, thereby maintaining system operation capability under sensor failure conditions.
Solution Approach 2:
The patent introduces intermediate calculation steps that use hand wheel angle and vehicle dynamics parameters as mediators to derive assist torque. Instead of directly using torque sensor outputs, the system uses these intermediate parameters to compute the required assist torque, providing a backup calculation path when primary sensors fail.
2Object-affected harmful factors
If the system switches to Limp Home mode when torque sensors fail, then safety is maintained, but vehicle operational capability is severely limited
Solution Approach 1:
The patent prepares alternative assist torque calculation methods in advance that can be activated when torque sensors fail. By having these backup calculation paths ready beforehand using hand wheel angle and vehicle dynamics data, the system cushions against the harmful effect of sensor failure and maintains full operational capability without needing to switch to limited Limp Home mode.
3Adaptability or versatility
If alternative assist torque calculation methods are implemented, then system functionality is maintained during sensor failure, but system complexity increases
Solution Approach 1:
The patent makes the control module universal by enabling it to perform multiple functions: normal assist torque calculation using torque sensors, and alternative assist torque calculation using hand wheel angle and vehicle dynamics parameters. This multi-functionality allows the same hardware to adapt to different operating conditions without adding separate dedicated systems, thereby limiting the increase in overall system complexity.
Data Source
AI summary
A method of controlling an electric power steering system of a vehicle is provided. The method determines that one or more hand wheel torque sensors of the vehicle are not enabled. The method generates an assist torque command by estimating a lateral acceleration of the vehicle based on a hand wheel angle and determining an amount of assist torque based on the estimated lateral acceleration. The method controls the electric power steering system using the generated assist torque command.