EPS Current Ramp Control for Auto Stop Transitions
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Solution Overview
Problem
Sudden changes in steering efforts during engine auto stop and start events in micro hybrid vehicles can cause driver dissatisfaction, and the battery may be overloaded when used to power the electric power steering assist system for extended periods.
Innovation Solution
Implementing a controller-based strategy to gradually reduce and increase the electric power steering system current before and after engine auto stops and starts, using different ramp rates to manage the transition from alternator to battery power, ensuring smooth steering assistance and preventing battery overload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric power steering system current is suddenly reduced during engine auto stop, then the battery overload is prevented, but the driver experiences sudden steering effort changes causing dissatisfaction
Solution Approach 1:
The patent applies dynamics by making the power steering assist variable rather than fixed. The controller dynamically adjusts the available electric power steering system current based on engine operating conditions (running vs. stopped). When the engine stops, the controller reduces the current limit from maximum to zero, allowing the system to adapt its performance characteristics to match the changing power availability conditions, thus preventing battery overload while managing steering effort transitions.
Solution Approach 2:
The patent changes the electrical parameter (available current) of the power steering system based on engine state. By monitoring engine running status and adjusting the current limit parameter accordingly - maintaining maximum current when engine runs and reducing to zero when engine stops - the system resolves the contradiction between preventing battery overload and maintaining steering smoothness through controlled parameter transitions.
2Ease of operation
If the electric power steering system uses maximum current during engine auto stop, then the steering assist performance is maintained, but the battery becomes overloaded
Solution Approach 1:
The patent implements feedback by having the controller continuously monitor engine operating conditions and use this information to adjust the available electric power steering system current. The controller receives feedback about engine state (running or stopped) and accordingly modifies the current limit - maintaining maximum current availability when the engine is running and reducing to zero when stopped, thus preventing battery overload while optimizing steering assist performance based on real-time system capabilities.
Solution Approach 2:
The system dynamically adapts its power consumption characteristics to match available power sources. When the engine is running, the power steering system operates with maximum current availability. When the engine stops and the system transitions to battery power, the controller reduces current availability to prevent battery overload, creating a dynamic response that balances steering performance with power system capabilities.
3Loss of energy
If the engine auto stop duration is extended, then the fuel economy is improved, but the battery usage duration increases causing potential overload
Solution Approach 1:
The patent applies partial action by reducing the electric power steering current to a threshold value (而非完全关闭) during engine auto stop events. This partial current reduction provides just enough steering assist to maintain acceptable driver experience while significantly reducing battery power consumption compared to maintaining full current, thereby extending the acceptable duration of engine stop events and improving overall fuel economy.
Solution Approach 2:
The system changes the electrical parameter (available current) based on engine operation state. During extended engine stop events, the controller maintains a reduced current threshold level rather than maximum current, optimizing the balance between providing sufficient steering assist and limiting battery usage duration to prevent overload, thus enabling longer beneficial engine stop periods for fuel economy.
Data Source
AI summary
An automotive vehicle may include an engine, an electric power steering system and at least one controller. The at least one controller may, during an auto stop event of the engine, reduce at a first rate an available electric power steering system current to a non-zero threshold value before fuel to the engine is shut off and reduce at a second rate different than the first rate the available electric power steering system current from the non-zero threshold value to 0 after fuel to the engine is shut off.