Handwheel Actuator Motor Stator for Passive Drag Torque
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Solution Overview
Problem
Steer-by-wire systems in vehicles lack a reliable mechanism to provide resistance to the handwheel rotation when the system is unpowered or faulty, which can lead to unsafe and unstable steering conditions.
Innovation Solution
A handwheel actuator assembly with a motor stator comprising a stack of laminations and conductive pins that allow axial current flow, generating drag torque through eddy and hysteresis losses, providing resistance even without electrical power and minimizing the need for additional components or electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If laminations are stacked with insulating coating to prevent axial current flow, then energy losses are reduced and drag torque is minimized, but resistance to handwheel rotation during power loss is insufficient
Solution Approach 1:
The patent applies different electrical conductivity properties to different parts of the stator. The bridge sections are made electrically conductive to allow axial current flow and generate drag torque, while the yoke sections maintain insulating properties to minimize eddy current losses. This local differentiation resolves the contradiction between minimizing energy losses and providing sufficient resistance during power loss.
Solution Approach 2:
The patent converts what would normally be harmful eddy currents into a beneficial safety feature. By allowing controlled axial current flow through conductive bridge sections, the system generates drag torque that provides resistance during power loss, transforming potential energy waste into a safety mechanism that prevents uncontrolled handwheel rotation.
2Reliability
If conductive pins are added to allow axial current flow, then drag torque is generated providing resistance, but manufacturing complexity increases
Solution Approach 1:
The patent merges the structural support function and the electrical conduction function into a single component - the bridge sections. These bridges are made from conductive material that both mechanically supports the lamination stack and electrically connects adjacent laminations axially, eliminating the need for separate conductive pins or fasteners and simplifying manufacturing.
Solution Approach 2:
The bridge sections serve multiple functions simultaneously: they provide mechanical support for the lamination stack, enable axial current flow for drag torque generation, and structurally connect adjacent laminations. This multi-functionality reduces the number of separate components needed and simplifies the overall manufacturing process.
3Reliability
If additional components are added to provide resistance, then safety is improved, but device complexity increases
Solution Approach 1:
The motor's own structure is modified to provide the safety function. The conductive bridge sections are integrated into the stator laminations, allowing the motor to generate drag torque and provide resistance during power loss using its inherent electromagnetic properties, without requiring external braking mechanisms or additional safety components.
Solution Approach 2:
The safety function is merged with the existing motor structure. The bridge sections that are already part of the stator assembly are made conductive to provide drag torque, eliminating the need for separate safety devices and reducing overall system complexity while maintaining improved reliability.
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
The solution ensures a significant level of resistance to handwheel rotation, enhancing safety and stability by providing a substantial drag torque that can be maintained without external power, thus preventing uncontrolled wheel rotation during faults or power loss.
Implementation Method 1
currents are prevented from flowing axially through the stator. This reduces energy losses within the motor that would otherwise result from current flowing axially in the stator
Implementation Method 2
generating drag torque through eddy and hysteresis losses
Data Source
AI summary
A motor includes a stator and a rotor. The stator carries a plurality of phase windings and the rotor carries a plurality of magnet poles. The stator has a stack of laminations which each have a ferromagnetic plate. Each lamination includes at least one hole within the plate that is aligned with a corresponding hole in adjacent plates in the stack. At least one electrically conductive pin extends axially along a length of the stator passing through the aligned holes to provide a path for currents axially along the stator.