Electric Power Steering Motor Current Limiting via Speed-Based Temperature Estimation
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Solution Overview
Problem
Conventional electric power steering devices face challenges in accurately limiting motor current without ambient temperature detection, leading to excessive current limitation and reduced steering assistance, especially when the motor and controller are located outside the vehicle compartment or affected by external factors like air streams and engine heat.
Innovation Solution
The electric power steering device employs a vehicle speed-based ambient temperature estimation using a vehicle speed-ambient temperature relation data referring unit and low-pass filtering to determine a motor current limiting value, allowing for accurate current limitation without the need for ambient temperature detecting means, and continues CPU power supply during engine cooling to maintain suitable motor current limiting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ambient temperature detecting means is used to determine motor current limiting value, then current limiting accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an ambient temperature estimating means that uses vehicle speed as an intermediary parameter to infer ambient temperature. Instead of directly measuring temperature with sensors, the system uses the relationship between vehicle speed and ambient temperature (higher speed correlates with lower ambient temperature due to air flow) to estimate the current ambient temperature, thereby avoiding the need for physical temperature detecting means while still achieving accurate current limiting
Solution Approach 2:
The patent replaces the mechanical/physical ambient temperature detecting means (temperature sensors) with an estimation system based on vehicle speed detection. The controller substitutes direct temperature measurement with an estimation algorithm that calculates ambient temperature based on detected vehicle speed, eliminating the need for separate temperature sensing hardware
2Device complexity
If maximum temperature in use is assumed without ambient temperature detection, then device complexity is reduced, but motor current is excessively limited and steering assistance effectiveness decreases
Solution Approach 1:
The patent implements dynamic current limiting by continuously adjusting the motor current limiting value based on real-time vehicle speed detection. As vehicle speed changes, the estimated ambient temperature changes, and the current limiting value is dynamically adjusted accordingly. This replaces the static assumption of maximum temperature with a dynamic estimation that adapts to actual operating conditions, preventing excessive current limitation while maintaining device simplicity
Solution Approach 2:
The system uses the vehicle's own operating parameters (vehicle speed) to estimate ambient temperature and determine appropriate current limiting values. The controller leverages information already available from the vehicle's operation to self-regulate motor current without requiring external temperature sensors or complex additional systems
3Ease of manufacture
If motor and controller are located outside vehicle compartment, then ease of manufacture is improved, but ambient temperature detection accuracy worsens due to air stream and engine heat effects
Solution Approach 1:
The patent uses vehicle speed as an intermediary parameter that indirectly reflects ambient temperature conditions. Since vehicle speed correlates with air flow and cooling effects on externally mounted components, it serves as a reliable proxy for estimating the thermal environment without requiring direct temperature measurement that would be affected by localized heat sources or air streams
Data Source
AI summary
An electric power steering device that can estimate an ambient temperature and apply current limiting without using ambient temperature detecting means is provided. The electric power steering device includes a motor that supplements the driver's steering force, a controller that determines and controls the quantity of current passed to the motor, and vehicle speed detecting means. The electric power steering device includes ambient temperature estimating means provided with a vehicle speed signal input from the vehicle speed detecting means and limits the quantity of current passed to the motor according to an output from the ambient temperature estimating means.