Electric Power Steering Return Control Asymmetry
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Solution Overview
Problem
Conventional electric power steering devices exhibit a left/right difference in the remaining steering angle near the neutral position due to asymmetry in the steering system, leading to incomplete return of the steering wheel when turned leftward, despite calculations based on steering angle for return control.
Innovation Solution
An electric power steering device that includes a basic return command value calculation unit, a turn/return determination unit, a gradually changing return command value calculation unit, and a return command value calculation unit, which calculates and adds a gradually changing return command value to the basic return command value to drive the electric motor, addressing the asymmetry and improving returnability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If steering wheel return control is executed using basic return command value calculated from steering angle, then the control system remains simple, but left/right difference in remaining steering angle occurs due to steering system asymmetry
Solution Approach 1:
The patent applies local quality by introducing a gradually changing return command value that specifically addresses the asymmetric characteristics of the steering system on the leftward turning side. This gradual increase in return command value during steering wheel return compensates for the frictional resistance that prevents complete return to neutral position, while maintaining simple control on the rightward side where the basic return command suffices.
Solution Approach 2:
The patent implements dynamics by making the return command value dynamic rather than static. The return command value gradually increases during the steering wheel return process, adapting to the changing frictional conditions as the steering wheel approaches the neutral position. This dynamic adjustment ensures complete return without requiring complex asymmetric control parameters.
2Manufacturing precision
If gradually increasing return command value is added to compensate for steering system asymmetry, then left/right difference in remaining steering angle is reduced, but control calculation complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-defining the gradual increase pattern of the return command value based on steering angle and rotational speed. This predetermined approach allows the control system to automatically compensate for asymmetric friction without requiring complex real-time calculations or additional sensors, thereby maintaining computational simplicity while achieving precise steering wheel return.
3Reliability
If return control is executed at low vehicle speeds, then steering wheel returnability is improved, but frictional resistance in steering system increases
Solution Approach 1:
The patent implements dynamics by making the return command value speed-dependent. At low vehicle speeds where frictional resistance is high, the gradually increasing return command value provides additional torque to overcome friction and ensure complete steering wheel return. As vehicle speed increases and friction decreases, the gradual increase pattern becomes less pronounced, maintaining smooth operation without excessive force.
Data Source
AI summary
An electric power steering device includes a basic return command value calculation unit configured to calculate a basic return command value in a direction to return a steering wheel to a neutral position on the basis of a steering angle of a steering wheel, a turn/return determination unit configured to determine the turn and the return of the steering wheel, a gradually changing return command value calculation unit configured to calculate a gradually changing return command value, the gradually changing return command value gradually increasing, while the return of the steering wheel is determined by the turn/return determination unit, and a return command value calculation unit configured to calculate a return command value by adding the gradually changing return command value to the basic return command value. The electric motor is driven by adding the return command value to the assist command value.