EPAS Motor Control via Segmented Overlay Torque
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Solution Overview
Problem
Existing electric power assisted steering (EPAS) systems face challenges in providing a consistent feel to the driver due to non-linear boost curves, which affect the amount of torque required to overcome overlay torque demands, leading to varying steering behavior based on the driver's effort.
Innovation Solution
A method and system that calculate a combined assistance force by applying a non-linear boost function to the user-applied torque and overlay force demand, ensuring the change in total force is independent of the user's torque input, thereby maintaining a consistent driver feel across different steering efforts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a non-linear boost function is applied to the user-applied torque to provide assistance, then the assistance torque is improved, but the consistency of driver feel deteriorates
Solution Approach 1:
The overlay force demand is segmented into two distinct components: a first component that is combined with user-applied torque before the non-linear boost function, and a second component that is combined after the boost function. This segmentation allows each component to be processed differently through the non-linear function, enabling the system to maintain improved assistance torque while preserving driver feel consistency across different steering conditions.
2Adaptability or versatility
If overlay torque demand varies with driver input to provide adaptive assistance, then the adaptability is improved, but the steering behavior consistency deteriorates
Solution Approach 1:
The system dynamically adjusts the overlay force demand based on driver input torque, with the first component being processed through the non-linear boost function along with user torque. This dynamic adaptation allows the system to respond appropriately to varying driver needs while the dual-component structure ensures that the second component maintains consistency in the overall steering behavior, resolving the contradiction between adaptability and consistency.
Data Source
AI summary
A method of controlling an electric motor in an electric power assisted steering system, the motor being arranged so as to apply a force to part of a steering mechanism of a vehicle, in which the method comprises calculating a force demand indicative of an assistance force dependent upon the torque applied by a user (TD) to the steering mechanism that it is to be applied to the steering mechanism to reduce the exertion required by the user to steer the vehicle; combining the force demand with an overlay force demand (TER) indicative of a force which it is desired to overlay over the assistance force, to generate a combined assistance force (TA); and controlling the motor according to the combined assistance force, such that together with the force applied by the user, a total force is applied to the steering mechanism, in which, in order to generate the combined assistance force the torque applied by the user is subjected to a non-linear boost function and in which the overlay force demand is combined with the force demand such that, for an arbitrary change in the overlay force demand the change in the total force is independent of the torque applied by the user over a range of torques applied by the user.