Handwheel Actuator Winding Damping for Steer-by-Wire Fail-Safe Torque
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Solution Overview
Problem
Steer-by-wire (SbW) systems suffer from low damping under power failure and off conditions, posing safety concerns due to the absence of mechanical coupling between the handwheel and steering rack, and existing strategies for passive damping may lead to undesirable behavior, high short circuit currents, and interference with normal operation.
Innovation Solution
Optimize the winding design of permanent magnet synchronous machines (PMSMs) in SbW systems by strategically shorting subsets of windings at obtuse angles and using MOSFETs to vary resistance based on vehicle speed, ensuring optimal damping characteristics without interfering with normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If existing strategies for passive damping are applied in SbW systems, then damping torque is provided, but high short circuit currents and interference with normal operation occur
Solution Approach 1:
The motor windings are divided into multiple subsets (first subset, second subset, third subset) with different resistance values. By selectively shorting specific subsets based on operating conditions, the patent provides damping torque while controlling short circuit currents. The segmentation allows different winding subsets to be activated depending on whether the system is in normal operation or fail-safe mode, thereby preventing harmful current spikes.
Solution Approach 2:
The patent dynamically adjusts which winding subsets are shorted based on the operational state of the SbW system. During normal operation, no windings are shorted to avoid interference. During fail-safe mode, specific subsets are shorted to provide passive damping. This dynamic reconfiguration allows the system to adapt its damping characteristics while minimizing harmful effects under different conditions.
2Reliability
If passive damping is implemented in SbW systems, then safety is improved under power failure, but interference with normal operation and stability loss occur
Solution Approach 1:
The windings are segmented into multiple subsets with different resistance values, allowing selective activation during fail-safe conditions. This segmentation ensures that damping is only applied when needed (improving safety) while leaving the system undisturbed during normal operation (maintaining stability).
Solution Approach 2:
The patent changes the resistance parameter of the motor windings by selectively shorting different subsets based on operational mode. During normal operation, all windings maintain their designed resistance values for optimal performance and stability. During power failure, specific subsets are shorted to change the effective resistance and provide passive damping, thereby improving safety without compromising normal operation stability.
3Force
If winding resistance is adjusted to provide damping, then damping torque increases, but interference with normal operation occurs
Solution Approach 1:
The system dynamically reconfigures the winding connections based on operational state. During normal operation, the MOSFETs keep all windings in their standard configuration, ensuring ease of operation and optimal motor performance. During fail-safe mode, the MOSFETs reconfigure to short specific winding subsets, providing damping torque without affecting normal operation characteristics.
Solution Approach 2:
The damping function is extracted as a separate, conditionally activated feature. By using MOSFETs to selectively short only specific winding subsets during fail-safe mode, the patent isolates the damping function from normal operation. This extraction ensures that damping torque is provided only when needed, without interfering with the ease of operation during normal conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Provides required damping/braking torque while maintaining normal operation, reducing interference and stability loss, and enabling enhanced active torque generation by optimizing winding configurations and using depletion/enhanced mode MOSFETs to tune damping characteristics.
Implementation Method 1
providing, in series with the subset of windings, at least one metal-oxide-semiconductor field-effect transistor (MOSFET) configured to: vary the resistance associated with the subset of windings based on a vehicle speed; and tune a damping characteristic associated with the handwheel actuator
Implementation Method 2
shorting a subset of windings of the number of windings, each winding of the subset of windings being disposed at an obtuse angle from each other winding of the subset of windings
Data Source
AI summary
A method for passive damping in a steer-by-wire handwheel actuator includes selecting a number of windings for a motor of a handwheel actuator; shorting a subset of windings of the number of windings, each winding of the subset of windings being disposed at an obtuse angle from each other winding of the subset of windings; determining a resistance value for the motor; selectively adjusting the resistance value based on a number of windings associated with the subset of windings; and providing, in series with the subset of windings, at least one metal-oxide-semiconductor field-effect transistor (MOSFET) configured to: vary the resistance associated with the subset of windings based on a vehicle speed; and tune a damping characteristic associated with the handwheel actuator.