Handwheel Actuator Drag Torque via Stator Segmentation
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Solution Overview
Problem
Steer-by-wire systems in vehicles lack a reliable fail-safe mechanism to prevent free rotation of the handwheel in case of power loss or electrical faults, which can impair steering functionality and lead to unstable vehicle control.
Innovation Solution
A handwheel actuator assembly with a solid stator or a laminated stator configuration that includes electrical connections between laminations, providing a significant drag torque through eddy current and hysteresis losses, ensuring resistance to handwheel rotation even without electrical power, by incorporating conductive paths and weld lines to facilitate axial current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a laminated stator with electrically insulating coating is used to prevent axial current flow and reduce energy losses, then energy efficiency is improved, but drag torque is reduced to a level that cannot provide sufficient resistance during power loss
Solution Approach 1:
The stator is segmented into multiple laminations with selective electrical connectivity. Insulating coatings are applied to certain laminations to prevent axial current flow and reduce energy losses, while conductive paths are maintained in specific regions to generate drag torque during power loss through eddy currents and hysteresis
Solution Approach 2:
Different regions of the stator have different electrical properties. The insulating coating is applied locally to specific laminations rather than uniformly across the entire stator, creating zones with different electrical conductivity to simultaneously reduce energy losses and maintain fail-safe drag torque
2Force
If braking torque is created by active control of motor drive circuit to provide resistance to handwheel rotation, then resistance to movement is improved, but system complexity and dependency on electrical power are increased
Solution Approach 1:
The motor provides resistance to handwheel rotation through passive physical mechanisms (eddy currents and hysteresis in the stator) rather than active electronic control. When power is lost, the motor automatically generates drag torque through these inherent material properties, eliminating the need for complex control circuit intervention
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 provides a consistent and substantial resistance to handwheel rotation, maintaining stability and preventing free rotation during power outages or faults, thus ensuring safe steering capabilities and reducing heat buildup in the drive circuit.
Implementation Method 1
the stator of at least one of the motors is configured such that in the event that the control circuit is powered down or disconnected and the handwheel is rotated at 180 degrees per second the combination of motors overall provides a drag torque of at least 50 percent of the resistance to rotation of the shaft
Implementation Method 2
providing a significant drag torque through eddy current and hysteresis losses
Data Source
AI summary
A handwheel actuator assembly for a steer-by-wire system of a vehicle comprises a housing, a shaft rotatably mounted to the housing, the shaft connectable to a handwheel, and one or more motors each having a stator and a rotor. The stator carries a plurality of phase windings and the rotor carries a plurality of magnet poles and is connected to the shaft. A control circuit is adapted to control the current flowing into or out of each motor to cause a net torque to be applied to the shaft during normal operation. The stator of at least one of the motors is configured such that in the event that the control circuit is powered down or disconnected and the handwheel is rotated at 180 degrees per second, the combination of motors overall provides a drag torque of at least 50 percent of the resistance to rotation of the shaft and a torque at the handwheel of at least 2 Nm.