Redundant Microcomputer Motor Control for Reliable IG-Off Transitions
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Solution Overview
Problem
Conventional motor control apparatuses face challenges in ensuring seamless operation and reliability when one microcomputer fails, particularly in electric power steering systems, due to variations in assist torque and potential erroneous failure determinations during IG-OFF transitions.
Innovation Solution
A motor control apparatus with redundant microcomputer systems and power supply relays, where inter-microcomputer communication ensures synchronized IG-OFF and re-IG-ON determinations, allowing for gradual current reduction and power latch processes to maintain system reliability and prevent erroneous stoppages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant microcomputer systems are used to ensure continuous operation, then system reliability is improved, but variations in assist torque occur during failure transitions
Solution Approach 1:
The patent applies preliminary action by having the normal microcomputer determine IG-OFF in advance before the abnormal microcomputer fails. This proactive determination allows the system to prepare for the transition by gradually reducing current and coordinating power supply relay operations, thereby preventing assist torque variations that would otherwise occur during sudden failure transitions.
Solution Approach 2:
The patent implements feedback through inter-microcomputer communication where the normal microcomputer receives determination signals from the abnormal microcomputer and adjusts its IG-OFF timing accordingly. This feedback mechanism ensures both microcomputers coordinate their shutdown actions, maintaining consistent assist torque throughout the failure transition process.
2Ease of operation
If microcomputers independently determine IG-OFF status, then system autonomy is maintained, but erroneous failure determinations occur
Solution Approach 1:
The patent uses feedback through inter-microcomputer communication signals where each microcomputer shares its IG-OFF determination status with the other. The normal microcomputer receives determination signals from the abnormal microcomputer and uses this feedback to verify its own determination, preventing erroneous failure determinations while maintaining system autonomy.
Solution Approach 2:
The patent introduces an intermediary communication mechanism between microcomputers that mediates the IG-OFF determination process. Through exchanging determination signals, the microcomputers collectively verify failure status before initiating shutdown, eliminating false positives while preserving individual system autonomy.
3Speed
If rapid IG-OFF determination is implemented, then response speed is improved, but assist torque variations occur during transition
Solution Approach 1:
The patent applies preliminary action by implementing a gradual current reduction process that begins immediately when IG-OFF is determined. This preliminary current ramp-down prepares the motor for shutdown, ensuring smooth transition without assist torque variations even though the IG-OFF determination itself is rapid.
Solution Approach 2:
The patent uses dynamics by making the current reduction rate adjustable based on system state. During rapid IG-OFF determination, the system dynamically controls the current decay profile to match the speed of determination, maintaining assist torque stability throughout the transition process.
Data Source
AI summary
Each of a plurality of microcomputers outputs a motor drive signal, which is generated based on a current command value and a current limit value as a control amount command value and a control amount limit value, to each motor drive circuit. When an OFF determination of an own microcomputer is made, each microcomputer executes first end processing as a first stage of end processing and transmits an OFF determination signal to the other microcomputer. When the OFF determination signal is received from the other microcomputer, each microcomputer determines that the OFF determination has been made and starts second end processing which gradually decreases the current command value or the current control limit value from a present value. When the second end processing is completed and power-off preparation of the own microcomputer and the other microcomputer is completed, each microcomputer executes final end processing for turning off the power supply relay.