Steer-By-Wire Differential Gear Redundancy for Actuator Failure
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Solution Overview
Problem
Steer-by-wire systems face safety issues due to the inability to perform steering control during mechanical failures of the actuator in the wheel steering mechanism, leading to potential accidents.
Innovation Solution
A redundancy structure is implemented in the steer-by-wire device, utilizing a differential gear module with two sun gears and a planet gear that can rotate about an axis of revolution, along with actuators and controllers to ensure steering control even in the event of mechanical failures, and locking units to prevent power dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single actuator is used in the wheel steering mechanism, then the device complexity is reduced, but the reliability deteriorates because steering control cannot be maintained during mechanical failures
Solution Approach 1:
The single actuator is segmented into two independent actuators (first actuator and second actuator), each capable of independently controlling the steering mechanism. This segmentation allows the system to maintain steering control even if one actuator fails, thereby improving reliability while managing complexity through functional division
Solution Approach 2:
Each actuator is designed with specific localized functions - the first actuator controls the first sun gear while the second actuator controls the second sun gear. This local quality differentiation enables independent operation and failure isolation, allowing the system to maintain overall functionality even when one local component fails
2Reliability
If a redundancy structure with two sun gears and planet gear is implemented, then the reliability is improved for coping with mechanical failures, but the device complexity increases
Solution Approach 1:
The differential gear module merges two sun gears and planet gears into a single integrated mechanical unit where the first sun gear, second sun gear, and planet gear work together through mechanical engagement. This merging allows the redundancy structure to achieve failure tolerance while managing complexity through unified mechanical design
Solution Approach 2:
The planet gear serves multiple functions: it transmits power from the first sun gear to the second sun gear, enables differential motion between the two actuators, and provides mechanical redundancy. This multi-functionality allows the system to achieve reliability improvement without proportionally increasing device complexity
3Reliability
If locking units are added to prevent power dispersion, then the reliability is improved by preventing harmful effects, but the device complexity increases
Solution Approach 1:
The locking units are designed to automatically engage or disengage based on the operational state of the actuators, performing the power isolation action preliminarily or automatically without requiring complex external control systems. This preliminary action capability improves reliability by preventing power dispersion while managing complexity through automatic control mechanisms
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 system maintains steering control by switching actuators and allowing the inoperative sun gear to be rotated, ensuring safe operation even with actuator breakdowns without increasing spatial constraints.
Implementation Method 1
a rack shaft, where a rack gear is mounted, configured to adjust steering angles of vehicle wheels by a linear motion of the rack gear; a pinion gear configured to move the rack gear linearly according to a rotational motion of the pinion gear engaged with the rack gear
Implementation Method 2
a differential gear module including (i) a 1-st sun gear and a 2-nd sun gear installed opposite each other, (ii) at least one planet gear, engaged with the 1-st sun gear and the 2-nd sun gear, wherein the planet gear revolves around an axis of revolution connecting a center point of the 1-st sun gear and a center point of the 2-nd sun gear
Data Source
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AI summary
A steer-by-wire device of a vehicle is provided. The steer-by-wire device includes: a rack shaft, where a rack gear is mounted, configured to adjust steering angles of vehicle wheels; a pinion gear configured to move the rack gear linearly according to a rotational motion of the pinion gear engaged with the rack gear; a differential gear module including (i) a 1-st and a 2-nd sun gears installed opposite each other, (ii) a planet gear, engaged with the 1-st and 2-nd sun gears, wherein the planet gear revolves in response to a rotational motion of the 1-st and/or the 2-nd sun gears, and (iii) a case configured to rotate according to a rotational motion of the planet gear; a 1-st and a 2-nd actuators for rotating the 1-st and the 2-nd sun gears; and a steering sensor configured to detect a momentum of the rack gear and/or the pinion gear.