Steer-by-Wire Travel Stop Assembly for Hand-Wheel Over-Rotation
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Solution Overview
Problem
The advancement in vehicle technology using hand-wheel actuators (HWA) and road-wheel actuators (RWA) leads to over-rotation issues, causing damage to components like the clock spring and air bag coil, as there is no mechanical linkage to limit rotation.
Innovation Solution
A travel stop assembly comprising a lead screw, nut, and stop pins within a housing that prevents excessive rotation by engaging stop arms with the nut to limit axial movement and rotation of the hand-wheel shaft, providing a 'hard stop' mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct mechanical linkage is used between hand-wheel and tires, then rotation of hand-wheel is limited preventing component damage, but the complexity of mechanical linkages increases
Solution Approach 1:
The patent extracts the rotation limiting function from the complex mechanical linkage system and implements it as a separate travel stop assembly. This assembly includes a lead screw, nut, stop pins, and stop arms that independently limit hand-wheel rotation without requiring complex mechanical linkages between the hand-wheel and tires. The stop pins engage with the stop arms to provide a simple mechanical constraint on rotation.
Solution Approach 2:
The patent introduces a travel stop assembly as an intermediary mechanism between the hand-wheel actuator and the steering column. This intermediary assembly includes a lead screw that converts rotational motion to linear motion of the nut, which then engages stop arms with stop pins to limit rotation. This intermediary mechanism provides rotation limiting without requiring direct complex mechanical linkages.
2Ease of operation
If hand-wheel actuator is used without mechanical linkage, then rotation control is lost causing over-rotation damage, but the simplicity of electrical control is reduced
Solution Approach 1:
The travel stop assembly is designed to be self-actuating through the lead screw and nut mechanism. When the hand-wheel rotates, the lead screw converts this rotation into linear movement of the nut, which automatically engages the stop arms with the stop pins at the predetermined rotation limit. This self-service mechanism provides automatic rotation control without requiring additional electrical sensors or actuators.
Solution Approach 2:
The patent replaces complex mechanical linkages with a simplified lead screw mechanism. The lead screw converts rotational motion to linear motion, providing a compact and simple mechanical solution for rotation control. This mechanical substitution maintains reliability while preserving the simplicity of electrical control architecture.
3Reliability
If stop pins engage stop arms to limit rotation, then component damage is prevented, but noise and vibration increase due to hard stop engagement
Solution Approach 1:
The patent positions the stop pins and stop arms to engage at the predetermined rotation limit before excessive rotation can occur. This beforehand engagement prevents the hand-wheel from reaching positions that would cause damage to components like the clock spring or air bag coil. The engagement point is carefully designed to stop rotation at the safe limit.
Solution Approach 2:
The patent allows the system to operate in two different states: free rotation during normal operation and constrained rotation when the stop is engaged. This parameter change from rotational freedom to rotational constraint provides effective protection while maintaining ease of operation during normal conditions. The stop mechanism transitions between these states based on the rotation angle.
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 travel stop assembly effectively limits hand-wheel rotation, preventing component damage while allowing free rotation in the opposite direction, offering a cost-effective and customizable solution for diverse customer demands, and reducing noise and vibration by minimizing moving parts.
Implementation Method 1
A nut that is in threaded engagement with the lead screw and axially movable along the lead screw upon a rotation of the lead screw
Data Source
AI summary
The present disclosure related to a travel stop assembly for preventing rotation, and undesired locking, of a shaft. The travel stop assembly may comprise a shaft that extends along an axis and is rotatable about the axis. A lead screw may extend along the axis and be operatively engaged, and rotatable, with the shaft about the axis. A nut may be in threaded engagement with the lead screw and axially movable along a length of the lead screw upon rotation of the lead screw. At least one stop pin may operatively engaged the lead screw and the at least one stop pin may extend from the lead screw perpendicularly relative to the axis. The stop pin may be positioned on the lead screw to stop rotation of the lead screw and the stop pin may prevent locking of the nut to the lead screw.