Dual-Motor Handwheel Assembly for Torque Ripple Cancellation
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Solution Overview
Problem
Steer-by-wire systems face issues with lack of resistance when the vehicle's wheels are at maximum steering angle, leading to unnatural control and potential inability to turn the wheel due to low mechanical friction and electromagnetic drag torque in handwheel actuator assemblies.
Innovation Solution
A dual motor handwheel actuator assembly with permanently magnet motors having the same number of poles and stators, where at least one phase of each motor is short-circuited to provide braking torque, and the motors are offset to cancel torque ripple, ensuring resistance and smooth operation even when unpowered or in fault conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If motors are designed with low mechanical friction and low electromagnetic drag torque for high efficiency, then energy conversion efficiency is improved, but resistance to wheel turning is reduced making the system feel extremely light and unnatural
Solution Approach 1:
The patent converts the harmful effect of low friction and low drag torque (which causes the wheel to feel extremely light and unnatural) into a beneficial feature by deliberately introducing controlled friction and electromagnetic drag through phase short-circuiting. This creates artificial resistance that mimics conventional steering systems while maintaining the underlying efficient motor design.
Solution Approach 2:
The patent changes the operational parameters of the motor by short-circuiting phases under specific conditions (unpowered state or fault conditions). This parameter change transforms the motor's characteristics from low-friction/high-efficiency mode to high-friction/artificial-resistance mode, providing natural steering feel when needed.
2Reliability
If dual motor system is used to provide fail-safe operation, then reliability is improved, but torque ripple affects the smoothness of operation
Solution Approach 1:
The patent introduces asymmetry in the motor configuration by deliberately offsetting the phases of the two motors relative to each other. This asymmetric phase arrangement causes the torque ripple from one motor to cancel the torque ripple from the other motor, resulting in smooth combined operation while maintaining the dual-motor fail-safe reliability.
Solution Approach 2:
The patent uses one motor to counterbalance the torque ripple effects of the other motor. By offsetting the phase angles, the disturbing torque ripple from one motor acts as a counterweight that cancels the ripple from the other motor, achieving smooth operation despite the presence of two separate motor systems.
3Reliability
If steering wheel rotation is limited to correspond to maximum steering angle, then safety is improved, but driver control flexibility is reduced when wheels are at maximum angle
Solution Approach 1:
The patent converts the harmful situation of the steering wheel feeling extremely light and turning too freely (when unpowered or in fault condition) into a beneficial safety feature. By introducing artificial resistance through phase short-circuiting, the system prevents indefinite wheel rotation even when motors are unpowered, thereby maintaining safety while allowing full rotational freedom.
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 natural feel and resistance to wheel turning by canceling torque ripple, ensuring the wheel can be controlled effectively even in fault conditions, enhancing safety and operational stability.
Implementation Method 1
first and second motors, each having an output driving a respective output gear
Implementation Method 2
both motors provided a braking torque as the driver turns the wheel
Implementation Method 3
the effect of torque ripple applied to the output shaft in the braking torque by the first motor is at least partially cancelled by the effect of torque ripple applied to the shaft in the braking torque by the second motor
Data Source
AI summary
A dual motor handwheel actuator assembly for a vehicle includes a housing. A shaft is rotatably mounted with respect to the housing and is configured for attachment of a steering wheel at one end. A first gear is connected to and configured to rotate with the shaft. Each of first and second motors has an output driving a respective output gear. The output gears are engaged with the first gear. Each motor includes a permanent magnet motor that has the same number of poles and stators such that each motor produces the same pattern of cogging torque over a complete mechanical revolution of the motor. The system is arranged so that in an unpowered condition where both motors are undriven at least one part of one of the phases of each motor is short circuited such that both motors provided a braking torque as the driver turns the wheel. The phases that include the short are selected according to the mechanical offset of the two motors relative to the output shaft whereby the effect of torque ripple applied to the output shaft in the braking torque by the first motor is at least partially cancelled by the effect of torque ripple applied to the shaft in the braking torque by the second motor.