Active Front Steering Current Limiting During Engine Auto-Stop
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Solution Overview
Problem
The integration of engine start-stop and active front steering systems in vehicles faces challenges in managing power demands during engine start-stop events, leading to voltage drops that can hinder the operation of electric power-assisted steering (EPAS) and active front steering (AFS) modules, resulting in reduced performance and potential failure to start the engine when propulsion is demanded.
Innovation Solution
The implementation of a controller-programmed electric actuator system that limits current draw during engine auto-stop events, ramps down current to a predetermined limit before fuel shutdown, and ramps up current as the engine restarts, along with a locking mechanism to prevent AFS assistance during auto-stop, ensuring reduced power consumption and maintaining steering functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric actuator operates at high current to provide active front steering assistance, then steering performance is improved, but voltage drops occur during engine start-stop events which can hinder engine restart and cause system failure
Solution Approach 1:
The patent implements dynamic current limiting where the controller adjusts the maximum current available to the electric actuator based on engine state. During start-stop events, the controller dynamically reduces the current limit to prevent voltage drops that would hinder engine restart, while allowing full current during normal operation to maintain steering performance
Solution Approach 2:
The system performs preliminary detection of engine start-stop events and proactively limits electric actuator current before the event occurs. The controller monitors engine state and prepares by reducing power availability to the AFS system in advance, preventing voltage drops before they can affect engine restart capability
2Reliability
If the electric actuator current is limited during engine auto-stop to prevent voltage drops, then engine restart reliability is improved, but steering assistance performance deteriorates
Solution Approach 1:
The system dynamically adjusts steering assistance based on engine state. During auto-stop events, the controller reduces electric actuator current to ensure engine restart reliability, while during normal operation, full steering assistance is restored. This dynamic adaptation resolves the contradiction by accepting temporary performance reduction only when necessary
Solution Approach 2:
The controller acts as an intermediary between the engine management system and the electric actuator. It translates engine state information into appropriate current limits for the actuator, mediating between the conflicting requirements of engine restart reliability and steering performance by selectively applying current limits only during critical start-stop transitions
3Loss of energy
If the controller limits electric actuator current during start-stop events, then power management is improved, but the complexity of coordinating multiple systems increases
Solution Approach 1:
The controller is designed to perform multiple functions: it manages electric actuator current limiting during start-stop events, monitors engine state, and coordinates with the engine management system. By consolidating these functions in a single controller, the patent reduces overall system complexity while achieving effective power management
Solution Approach 2:
The system implements feedback control where the controller continuously monitors engine state and electric actuator operation. Based on this feedback, the controller dynamically adjusts current limits to optimize power management during start-stop events, reducing energy loss while maintaining simple control logic through closed-loop operation
Data Source
AI summary
A vehicle includes an engine configured to auto stop and auto start. The vehicle includes an active front steering system with an electric actuator. A controller operates the electric actuator at a current limit that is less than a requested current of the electric actuator in response to a request to change a steering ratio by an amount that results in the requested current being greater than the current limit during an engine auto stop event. The current limit may decrease from the requested current to a predetermined limit after transitioning to the engine auto stop event. The current limit may increase from the predetermined limit to the requested current after transitioning from the engine auto stop event.