Compliant Shaft-Rotor Coupling for Smooth Steer-by-Wire End Stops
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Solution Overview
Problem
Steer-by-wire devices experience 'sticky' steering due to the lack of mechanical end stops, requiring operators to overcome peak torque to rotate the steering wheel beyond end positions, making maneuvering difficult.
Innovation Solution
A steer-by-wire device with a flexible coupling region between the input shaft and rotor, allowing relative movement and a magnetic field to generate torque, includes a flexible coupling region with gaps to enable rotation past end stops without overcoming maximum torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a magnetically-responsive rotor is attached to the output shaft with rigid connection, then torque can be effectively transmitted and end stop torque can be generated, but the steering wheel becomes stuck at end stops requiring excessive force to overcome
Solution Approach 1:
The patent employs a flexible coupling mechanism between the input shaft and rotor, utilizing flexible elements that allow relative movement. This flexibility enables the rotor to decouple from the input shaft when maximum torque is applied at end stops, preventing the steering wheel from becoming stuck while maintaining effective torque transmission during normal operation.
Solution Approach 2:
The coupling between the input shaft and rotor is made dynamic rather than rigid. The flexible coupling allows the system to adapt its stiffness characteristics based on operating conditions - providing rigid torque transmission during normal steering and allowing slip when end stop torque is applied, thereby resolving the contradiction between reliable torque generation and ease of operation.
2Reliability
If maximum electrical current is applied to generate peak end stop torque, then further rotary movement is prevented, but the steering wheel resists rotation in both directions creating sticky steering
Solution Approach 1:
The flexible coupling acts as a cushioning element that anticipates the problem of sticky steering. By allowing controlled slip between the input shaft and rotor when maximum torque is applied, the system prevents the buildup of excessive resistance that would otherwise make the steering wheel difficult to rotate in either direction from the end stop position.
Solution Approach 2:
The flexible coupling serves as an intermediary element between the input shaft and rotor. It mediates the interaction between the operator's steering input and the electromagnetic torque, allowing the system to enforce end stop conditions while preventing the steering wheel from becoming stuck through controlled relative movement.
3Ease of operation
If a direct physical linkage connects input device to output device, then mechanical end stops naturally prevent further travel, but in steer-by-wire applications physical connection is impractical or impossible
Solution Approach 1:
The patent replaces the traditional mechanical end stop linkage with an electromagnetic torque-based end stop mechanism. Instead of using physical stops and linkages to prevent further travel, the system uses a magnetically-responsive rotor with electromagnetic coils to generate torque that enforces end stop conditions, eliminating the need for direct physical connection between input and output devices.
Solution Approach 2:
The flexible coupling acts as an intermediary that bridges the gap between the electromagnetic torque system and the mechanical steering wheel. It allows the electromagnetic system to enforce end stop conditions without requiring direct mechanical linkage, thereby maintaining natural end stop indication while avoiding the complexity of physical linkages in steer-by-wire applications.
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
Enables smooth steering transitions by detecting angular position changes to terminate maximum torque, reducing 'sticky' steering and enhancing operator control.
Implementation Method 1
a coil configured to generate a magnetic field when a current is supplied to the coil, wherein the magnetic field generates a rotary force or torque in the rotor to resist rotation of the rotor
Implementation Method 2
A Hall effect sensor is typically provided in the input device of such steering systems to provide angular position information to a steering controller
Data Source
AI summary
A steer-by-wire device for controlling a vehicle includes a housing; an input shaft that is rotatable relative to the housing and is configured to receive a rotary input from an operator of the vehicle at a first end of the input shaft, the first end being located external to the housing; a rotor attached to the input shaft at a second, opposite, end of the input shaft, the second end being located internal to the housing; a sensor for detecting an angular position, an angular velocity, and/or an angular acceleration of the input shaft relative to the housing; and a coil for generating a magnetic field to generate a rotary force or torque in the rotor to resist rotation of the rotor. The rotor is attached to the input shaft to allow a relative movement between at least a portion of the rotor and the input shaft.