Motor Control Unit Steering Assist Discontinuity
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Solution Overview
Problem
Existing motor control units for electric power steering systems with multi-system motor windings face challenges in smoothly adjusting current command values when a failure occurs, leading to discontinuous steering feelings and inefficient heat management, with previous methods either setting overly high current values or using inflexible adjustment methods that cannot adapt to varying steering torques.
Innovation Solution
A motor control unit that dynamically adjusts the current command value by changing its characteristic from a first characteristic equivalent to the pre-failure total characteristic to a second characteristic with a gentler gradient, asymptotically converging near the maximum output, or saturating at the maximum output, and performing this change based on time, steering conditions, or assist maps, to minimize load and maintain smooth steering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the current command value is set to maintain pre-failure total characteristic after system failure, then the steering assist force is maintained, but the motor overheats due to excessive current load
Solution Approach 1:
The patent applies dynamics by transitioning the current command value characteristic from a static pre-failure total characteristic to a dynamic post-failure characteristic. The control unit changes the characteristic of the current command value from a first characteristic (equivalent to pre-failure total) to a second characteristic (with suppressed output) after detecting system failure, allowing the steering assist force to be maintained initially while preventing motor overheating through gradual current reduction.
Solution Approach 2:
The patent applies parameter changes by modifying the characteristic of the current command value parameter. The control unit changes the characteristic from a first characteristic that forms a total equivalent to pre-failure current command values to a second characteristic whose output is more suppressed. This parameter transformation allows the system to maintain steering assist while reducing current load to prevent overheating.
2Temperature
If the current command value is reduced to prevent motor overheating, then motor temperature is controlled, but the steering assist force becomes insufficient
Solution Approach 1:
The patent applies preliminary action by first establishing the first characteristic of the current command value that is equivalent to the pre-failure total characteristic, ensuring adequate steering assist force is maintained immediately after failure detection. Only after this preliminary establishment does the control unit transition to the second characteristic with suppressed output, ensuring the steering assist force is sufficient before gradually reducing current to control motor temperature.
3Device complexity
If a fixed multiplying factor is used to adjust the current command value, then the control method is simple, but the adjustment cannot adapt to varying steering torques and driving conditions
Solution Approach 1:
The patent applies dynamics by making the current command value adjustment adaptive rather than fixed. The control unit dynamically changes the characteristic of the current command value from a first characteristic to a second characteristic based on varying steering torques and driving conditions. This dynamic adaptation allows the system to respond appropriately to different operational scenarios while maintaining manageable control complexity through characteristic transformation.
4Ease of operation
If the current command value is adjusted gradually over time, then the steering feel becomes smooth, but the response time to reach the new steady state is extended
Solution Approach 1:
The patent applies preliminary action by first establishing the first characteristic of the current command value that provides adequate steering assist force immediately after failure detection. This preliminary establishment ensures rapid initial response, and only thereafter does the control unit transition to the second characteristic with suppressed output, balancing fast response with smooth steering feel through sequential characteristic changes.
Data Source
AI summary
[Problem]An object of the present invention is to provide a motor control unit that improves a discontinuous feeling of an assist by flexibly making an adjustment of a current command value of a normal system when a failure occurs in any system of multi-system motor control, and enables smooth handling, and to provide an electric power steering apparatus and a vehicle equipped with the same.[Means for Solving the Problem]A motor control unit comprises motor driving circuits of respective winding systems that supply a motor having multi-system motor windings with driving currents; and a control calculating section that calculates a current command value of each winding system for driving the motor, when a failure occurs in the motor winding or the motor driving circuit in any of the systems, performs a first change of changing a characteristic of the current command value of a normal system to a first characteristic that forms a characteristic equivalent to a total of the current command values at normal time, after performing the first change, performs a second change of changing the characteristic of the current command value to a second characteristic whose output is more suppressed than the first characteristic, and controls the motor driving circuit.