Electric Power Steering Damping Function for Engine Start Voltage Stability
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Solution Overview
Problem
Modern electric power steering systems face challenges in providing reliable steering assistance during the start-stop cycles of internal combustion engines, leading to dips in on-board electric system supply voltage and potentially disrupting the driver's steering experience.
Innovation Solution
The method involves reducing the assistance torque of the electric power steering system using a damping function when the internal combustion engine starts, which is controlled by an electronic control unit based on state variables such as rotor speed and supply voltage, ensuring a gentle reduction in steering assistance to prevent voltage drops and maintain a natural steering sensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the assistance torque is maintained at normal levels during engine starting, then the steering assistance remains strong and natural, but the supply voltage of the on-board electric system drops due to high current demand from the starter motor
Solution Approach 1:
The assistance torque is dynamically adjusted based on the engine starting state. The control unit detects when the engine is starting and automatically reduces the assistance torque to a reduced level, then restores it to the normal level when starting is complete. This dynamic adaptation resolves the contradiction by making the steering system flexible enough to accommodate voltage variations during engine starting while maintaining normal steering assistance during regular operation.
Solution Approach 2:
The assistance torque parameter is changed from its normal value to a reduced value during engine starting. The control unit modifies the torque parameter based on the detected engine state, thereby adapting the steering system's electrical demand to match the available power supply capacity during critical starting operations.
2Object-affected harmful factors
If the assistance torque is reduced during engine starting, then the supply voltage remains stable, but the steering sensation becomes less natural and more difficult for the driver
Solution Approach 1:
The system dynamically switches between two torque levels based on engine state. During starting, the reduced torque prevents voltage dips. When starting is complete, the torque automatically returns to the normal level, restoring natural steering sensation. This temporal separation ensures that the compromised steering ease is limited only to the brief starting period.
Solution Approach 2:
The control unit detects the engine starting state in advance and proactively reduces the assistance torque before voltage dips can occur. This preliminary action prevents the harmful voltage fluctuation while maintaining steering functionality, and subsequently restores full assistance once the starting event is complete.
3Object-affected harmful factors
If the assistance torque is abruptly reduced during engine starting, then the voltage stabilization is immediate, but the steering feel becomes jerky and unpleasant for the driver
Solution Approach 1:
The control unit applies a damping function that gradually reduces the assistance torque over time rather than making an abrupt change. This cushioning approach prevents sudden jumps in steering feel while still achieving voltage stabilization during engine starting. The gradual transition ensures smooth steering characteristics are maintained even as torque is reduced.
Solution Approach 2:
The assistance torque is reduced in a controlled, time-based manner during the starting event. The control unit implements a periodic adjustment strategy where the torque reduction follows a predetermined profile that balances voltage stabilization needs with steering smoothness requirements, then restores torque in a similarly controlled manner after starting.
Data Source
AI summary
A method for operating an electrical power steering system of a transportation vehicle wherein a steering wheel angle is pre-defined by a steering wheel as a measure for a desired wheel steering angle for at least one steerable wheel of the transportation vehicle, where an electrical power drive with an electric motor provides a steering support, and where a support torque of the steering support is reduced based on a damping function in response to the combustion engine of the transportation vehicle being started. Also disclosed is an associated electrical power steering system, to a computer program, and to a control appliance.