Electric Power Steering Controller Torque Ripple Mitigation
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Solution Overview
Problem
Conventional electric power steering systems experience a decrease in steering feel and torque due to power drops and torque ripples when an energization failure occurs, limiting continuous power assist control.
Innovation Solution
An electric power steering system with dual-system motor coils and a controller that prioritizes power supply to maintain torque characteristics by using two phases as energized phases when one system fails, and adjusts power supply based on vehicle speed to minimize torque ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two-phase drive control is used after energization failure, then continuous power assist control is maintained, but torque ripples significantly increase
Solution Approach 1:
The patent applies parameter changes by switching from secant/cosecant current patterns to sinusoidal current patterns after energization failure. This changes the electrical parameters (current waveform, frequency, phase) to minimize torque ripples while maintaining continuous power assist control. The sinusoidal pattern provides smoother torque delivery compared to the sharp variations in secant/cosecant patterns.
Solution Approach 2:
The patent implements dynamic control by continuously adjusting the current commands to both driver circuits based on real-time feedback. The control signals are dynamically modified to compensate for the failed phase, using the remaining healthy phases to generate the required torque while maintaining smooth operation and minimizing ripples through active feedback control.
2Reliability
If dual-system motor coils are used, then continuous power assist control is maintained after failure, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the dual-system motor coils and driver circuits to serve multiple functions: normal three-phase operation, fallback to two-phase operation after failure, and active redundancy for continued assistance. The same hardware infrastructure supports both primary and backup operational modes, maximizing the utility of the added complexity.
Solution Approach 2:
The patent applies segmentation by dividing the motor coil system into two independent dual-system sets, each with its own driver circuit. This segmentation allows one system to fail while the other continues operation, and enables flexible reconfiguration of which phases are active based on failure detection, thereby maintaining functionality while managing complexity through modular design.
3Reliability
If phase current is limited near asymptote, then current safety is maintained, but motor torque drops
Solution Approach 1:
The patent applies the intermediary principle by using the second driver circuit as a mediator to compensate for torque loss when the first driver circuit's current is limited. When one phase approaches its current limit near the asymptote, the control system activates or increases current in the other healthy phases through the second driver circuit, effectively mediating the torque delivery to maintain overall motor torque while respecting individual phase current limits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system prevents power drops and reduces torque ripples, improving steering feel during continuous control after an energization failure without upsizing components.
Implementation Method 1
a steering force assist device that gives assist force to a steering system based on magnetomotive force that is generated by dual-system motor coils
Data Source
AI summary
In an electric power steering system, a control signal output section outputs independent dual-system control signals to driver circuits that are disposed in connection with independent dual-system motor coils. The control signal output section gives high priority to the output of the control signal to the other system, when the occurrence of energization failure is detected in one system. When the energization failure occurring phase is only one phase and the value of the basic command exceeds the upper limit of the priority command, the control signal output section outputs the control signal to the driver circuit in the system where the energization failure has occurred in order to supply electric power in which the two phases other than the energization failure occurring phase are used as the energized phases on the bases of the complementary command that corresponds to the excess of the upper limit.