EPAS Motor Current Ramp Control for Auto Stop-Start Engines
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Solution Overview
Problem
Conventional electronic power assisted steering (EPAS) systems in vehicles with auto stop-start engines experience delays in ramping in current to the EPAS motor, leading to reduced powered assistance to the steering assembly, which affects drivability, performance, and customer satisfaction due to reliance on timer-based initiation based on steady state battery voltage.
Innovation Solution
The method involves determining a moving average voltage, voltage rate of change, and moving average engine speed to initiate the ramping in of current to the EPAS motor, allowing for earlier restoration of powered assistance by setting thresholds below steady state values, ensuring successful re-cranking and starting of the engine before providing EPAS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If timer-based initiation is used to ramp in current to the EPAS motor after auto stop, then the system ensures engine stability before providing power assistance, but this causes delays in restoring powered assistance to the steering assembly
Solution Approach 1:
The system changes the control parameters from fixed timer-based initiation to dynamic parameter monitoring. It continuously monitors battery voltage, voltage rate of change, and engine speed, using these varying parameters to determine the optimal time to ramp in current. This allows the system to restore power assistance as soon as conditions permit, rather than waiting for a predetermined time period.
Solution Approach 2:
The system implements feedback control by continuously monitoring battery voltage, voltage rate of change, and engine speed during the auto start sequence. These feedback signals are used to dynamically adjust the timing of current ramp-in to the EPAS motor, ensuring that power assistance is restored at the optimal moment when both engine stability and steering responsiveness are satisfied.
2Loss of time
If current is ramped in immediately after engine re-cranking, then powered assistance is restored quickly, but this may cause voltage instability or improper steering assistance during engine starting
Solution Approach 1:
The system uses battery voltage and voltage rate of change as intermediary indicators to mediate between the need for quick power assistance restoration and the need for voltage stability. By monitoring these intermediary parameters, the system can determine the safe moment to ramp in current, ensuring that the battery can support the additional load without instability.
Solution Approach 2:
The system performs preliminary monitoring of battery voltage, voltage rate of change, and engine speed during the engine start sequence before initiating current ramp-in to the EPAS motor. This preliminary action ensures that all necessary conditions are verified before restoring power assistance, preventing voltage instability or improper steering assistance.
3Device complexity
If steady state battery voltage thresholds are used to initiate current ramp-in, then the control logic is simple, but this causes unnecessary delays since voltage recovers continuously during engine start
Solution Approach 1:
The system transitions from static, fixed-threshold control logic to dynamic, continuous monitoring of multiple parameters. Instead of waiting for battery voltage to reach a predetermined steady state threshold, the system dynamically evaluates voltage, voltage rate of change, and engine speed in real-time, allowing current ramp-in to occur as soon as conditions are appropriate during the voltage recovery process.
Solution Approach 2:
The system performs preliminary monitoring and evaluation of battery voltage, voltage rate of change, and engine speed during the engine start sequence before initiating current ramp-in. This preliminary action allows the system to prepare for and execute current ramp-in at the optimal moment, reducing delays while maintaining simple control logic based on clear threshold criteria.
Data Source
AI summary
Methods and apparatus for controlling the ramp in of current to an electronic power assisted steering motor associated with an auto stop-start engine are described. A controller is to determine a moving average voltage of a vehicle battery. The controller is also to determine a voltage rate of change based on the moving average voltage. The controller is also to determine a moving average engine speed of an auto stop-start engine of the vehicle. The controller is also to ramp in current to an electronic power assisted steering motor of the vehicle based on the moving average voltage, the voltage rate of change, and the moving average engine speed.