Electric Power Steering Assist Control During Cranking Voltage Drops
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Solution Overview
Problem
Electric power steering systems face challenges in maintaining stable assist control during cranking, where power voltage drops can lead to uncomfortable steering behaviors and potential FET burnout, especially in vehicles with idling-stop functions.
Innovation Solution
An electric power steering apparatus that includes a power voltage monitoring section to determine the assist continuation permissible time and calculates an assist possible current limitation value using a current limiting map, allowing for controlled assist operations even during power voltage drops, thereby preventing uncomfortable steering experiences and FET damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If assist control is maintained during power voltage drop, then steering assist continuity is improved, but FET burnout risk increases
Solution Approach 1:
The patent implements dynamic assist control by continuously monitoring power voltage and adjusting assist availability in real-time. When voltage drops below threshold, the system transitions from normal assist mode to limited or disabled assist mode, preventing FET burnout while maintaining steering control during acceptable voltage conditions
Solution Approach 2:
The system employs feedback control through power voltage monitoring that continuously measures voltage levels and feeds this information back to the control unit. Based on the feedback, the system automatically adjusts assist control parameters to prevent operating conditions that would cause FET burnout
2Reliability
If assist amount is limited during power voltage drop, then FET safety is improved, but steering assist performance deteriorates
Solution Approach 1:
The patent changes operational parameters by adjusting assist control based on power voltage levels. When voltage drops, the system modifies assist current limits, duty cycle ratios, or enables/disables assist entirely, optimizing the balance between FET protection and steering performance under varying voltage conditions
3Reliability
If assist control is disabled during power voltage drop, then FET burnout is prevented, but steering behavior stability deteriorates
Solution Approach 1:
The system prepares for potential voltage drops by having pre-defined assist control strategies ready to activate. When voltage drop is detected, the system smoothly transitions to a controlled assist limitation mode rather than abrupt disablement, cushioning the impact on steering behavior stability
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 effectively suppresses steering assist variations and maintains assist control within safe limits during cranking, enhancing the overall performance and reliability of the electric power steering system.
Implementation Method 1
The adjustment of the voltage applied to the motor is generally performed by an adjustment of a duty ratio of a PWM (Pulse Width Modulation) control
Implementation Method 2
Electric power is supplied from the battery 14 as a power supply to the inverter 362 through the ignition key 11 and a power relay RL
Implementation Method 3
an inverter 362 comprising a three-phase bridge circuit of FET1 to FET6 and a step-up power supply 363 that drives high side FETs
Data Source
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AI summary
The present invention provides an electric power steering apparatus that is capable of suppressing behaviors of steering assist and performing assist control without an uncomfortable feeling even though a power voltage varied drastically during cranking. [Means for solving the problem] The electric power steering apparatus comprises a steering torque detecting means for detecting a steering torque applied to a steering mechanism, a motor for generating an assist force that assists steering of a steering wheel, a power voltage detecting means for detecting a power voltage of a power supply, a power voltage monitoring section for determining a power voltage detection value detected by the power voltage detecting means and a motor drive control means for calculating an assist amount based on the steering torque and controlling drive of the motor through a driving section comprising an FET-bridge, and assist control is maintained based on a drive possible characteristic corresponding to a reduction level of the power voltage of FETs when the power voltage monitoring section determines that the power voltage detection value is less than or equal to an assist operation possible power voltage.