Electric Power Steering Torque Modulation via Feedback Control
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Solution Overview
Problem
Conventional electric power steering systems in motor vehicles experience modulation issues due to non-homokinetic cardan joints, leading to uneven steering torque felt by the driver, especially during low-speed maneuvers, as the angles between cardan joint sections are not optimally aligned, causing cyclic modulations and an unpleasant steering experience.
Innovation Solution
An assembly for a motor vehicle that determines the intensity of electric current for electric power steering based on the steering wheel angle and pinion torque, incorporating a power steering control device to modulate the relationship between pinion and flywheel torque, ensuring the steering wheel torque remains within a predetermined limit by adjusting the assistance intensity, and using correction means to apply a variable corrective torque to the steering shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the steering shaft is divided into sections connected by simple universal joints, then the steering system can accommodate angular misalignments between sections, but cyclic modulations occur in the rotational speed of the driven section relative to the driving section, causing uneven steering torque felt by the driver
Solution Approach 1:
The control device measures the actual pinion torque and steering wheel angle, then uses this feedback information to calculate and apply a compensatory assist torque that counteracts the cyclic modulations generated by the non-homokinetic universal joints, ensuring smooth steering operation
Solution Approach 2:
The system dynamically adjusts the assist torque parameter based on the measured steering wheel angle and pinion torque, modifying the electrical assistance to compensate for the mechanical imperfections of the universal joints and maintain consistent steering characteristics
2Ease of manufacture
If the break angles between cardan joint sections are not equal or the universal joints are not optimally aligned, then the steering system can be manufactured with easier alignment tolerances, but the modulation of pinion torque to flywheel torque increases, causing hard and soft spots during steering
Solution Approach 1:
The invention replaces the mechanical solution of precise universal joint alignment with an electrical control system that calculates and compensates for torque modulations, allowing easier manufacturing tolerances while maintaining steering quality
Solution Approach 2:
The control device acts as an intermediary between the pinion torque and the electric assist, introducing a modulation term that compensates for the imperfect mechanical transmission through the universal joints, thereby smoothing the final steering torque
3Power
If the assist torque rapidly increases while pinion torque remains constant during low-speed maneuvers, then the electric power steering provides strong assistance for parking and cornering, but the steering wheel torque becomes uneven and unpleasant for the driver
Solution Approach 1:
The assist torque is made dynamic and adaptive, continuously adjusted based on real-time measurements of steering wheel angle and pinion torque, allowing the system to provide strong assistance when needed while maintaining smooth and regular steering characteristics through active compensation of cyclic modulations
Data Source
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AI summary
The invention relates to an assembly (100) for a motor vehicle, comprising: -a steering unit (10) comprising a rack (11); -a steering column (20) comprising a pinion (23) for applying to the rack a pinion torque (Cp), a steering wheel (22) attached to an upper end (24) of the steering column in order to apply to it a steering wheel torque (Cv), first measurement means (34) for measuring an angle of rotation of the steering column (αv), second measurement means (35) for measuring the pinion torque; -an electric power steering (40) for converting a power steering current intensity (Ia) into a power steering torque (Ca)or a power steering force to be applied to the rack; -at least one device for modulating the relationship between the pinion torque and the steering wheel torque, the steering wheel torque being equal to the pinion torque corrected by at least one modulation term that can vary at least according to the angle of rotation of the steering column; -a control device (50) for determining, from the steering wheel torque calculated at least as a function of the measured pinion torque and of the modulation term , the intensity of the power steering current to be delivered to the electric power steering.