Electric Power Steering Current Limiting for End Contact Impact
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power steering devices fail to adequately mitigate impact and deterioration in steering feeling on low μ roads, where the rack end collides with the rack housing due to limited torque current components, leading to increased impact and poor steering experience.
Innovation Solution
An electric power steering device with a control device that calculates current and voltage command values based on steering torque, incorporating q-axis and d-axis current command units to limit current values dynamically, preventing excessive steering angles and mitigating end contact impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the current command value is limited to a positive value only, then the assist torque is reduced to mitigate end contact impact, but the steering feeling deteriorates on low μ roads due to insufficient torque reduction
Solution Approach 1:
The patent changes the parameter of current command value from always positive to conditionally negative. When the steering angle exceeds the threshold angle, the current command value is set to a negative value proportional to the steering angle, rather than maintaining it as a positive value. This parameter change enables sufficient torque reduction to mitigate end contact impact while maintaining controllable steering characteristics.
Solution Approach 2:
The patent introduces dynamic adjustment of the current command value based on the steering angle. The control device dynamically switches between positive current command (when steering angle is within threshold) and negative current command (when steering angle exceeds threshold). This dynamic control adapts the assist torque to the actual steering state, resolving the contradiction between impact mitigation and steering feeling.
2Object-affected harmful factors
If the q-axis current limitation value decreases with increase in steering angle and becomes negative, then end contact impact is sufficiently mitigated, but the control complexity increases
Solution Approach 1:
The patent simplifies the control by changing the parameter definition of the q-axis current limitation value. Instead of using complex multi-stage limitation logic, the patent directly defines the limitation value as a negative value proportional to the steering angle when the threshold is exceeded. This parameter change reduces control complexity while achieving sufficient impact mitigation.
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 device effectively reduces end contact impacts and maintains a favorable steering feeling even on low μ roads by adjusting current and voltage limits based on steering angle and velocity, preventing collisions and enhancing steering performance.
Implementation Method 1
a motor 8 that generates an electromagnetic force
Implementation Method 2
a motor having a permanent magnet in a rotor
Implementation Method 3
AC current is decomposed into magnetic flux component current and torque component current by a method called coordinate conversion
Implementation Method 4
flux weakening control in which the magnetic flux component current is controlled so as to cancel out a magnetic flux of the rotor
Data Source
AI summary
In a control device of an electric power steering device, a q-axis current command value calculation unit which calculates a current command value for a motor for producing assist torque is provided with a q-axis current limitation value calculation unit which calculates a q-axis current limitation value such that, in a case where the absolute value of a steering angle is equal to or greater than a predetermined first steering angle threshold, the q-axis current limitation value decreases with increase in the absolute value of the steering angle, thereby restricting a q-axis current command value. Thus, a steering operation is prevented from being performed to a maximum steering angle θmax and impact by end contact can be mitigated.