Electric Power Steering Motor Current Compensation for Cold Weather Friction
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Solution Overview
Problem
Electric power steering systems face increased steering resistance due to contraction and viscosity changes at low temperatures, such as in winter, requiring enhanced motor current control to maintain efficient steering power.
Innovation Solution
An electric power steering apparatus with a temperature sensor, counter, friction coefficient determination unit, and target current calculation unit to measure initial temperature, calculate elapsed time, determine friction coefficient, and adjust motor current to compensate for increased friction, thereby enhancing auxiliary steering power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the motor supplies auxiliary steering power proportional to the generated steering torque, then energy efficiency is improved, but steering power is insufficient at low temperatures due to increased friction
Solution Approach 1:
The patent changes the motor current parameter based on temperature conditions. At low temperatures, the control unit increases the motor current beyond what would be normally required, compensating for the increased friction from contracted elements and viscous lubricating fluid. This allows the motor to provide sufficient steering power while maintaining energy efficiency by only increasing current when temperature conditions require it.
2Force
If the hydraulic pump always consumes energy, then auxiliary steering power is consistently available, but energy efficiency deteriorates
Solution Approach 1:
The electric power steering system provides auxiliary steering power only when needed, based on the steering torque generated by the driver. The motor operates proportionally to the actual steering requirement, allowing the system to be self-regulating and energy-efficient, unlike the hydraulic system that consumes energy continuously regardless of steering needs.
3Force
If the motor current is increased to compensate for low temperature friction, then steering power is improved, but energy consumption increases
Solution Approach 1:
The control unit uses temperature information as feedback to adjust motor current. The temperature sensor detects the ambient temperature, and the control unit uses this feedback to determine whether to increase motor current for friction compensation. This feedback mechanism ensures that energy is only consumed when temperature conditions require additional steering power, avoiding unnecessary energy waste at normal temperatures.
Data Source
AI summary
An electric power steering apparatus includes a temperature sensor measuring a temperature at a starting of a vehicle, a motor position sensor detecting a relative steering angle of a motor, a cumulative transfer calculation unit calculating a cumulative transfer quantity of a rack bar by information detected in the motor position sensor, a counter calculating an elapsed time from a starting time of the vehicle, a friction coefficient determination unit determining a friction coefficient according to information inputted from the temperature sensor, the cumulative transfer quantity calculation unit, and the counter, respectively, by using a setting map of a friction coefficient, and a target current calculation unit calculating a compensation quantity for a friction by using the friction coefficient determined in the friction coefficient determination unit and determining a target current.