Reversible Wiper Motor Motion Stops for Aircraft Sweep Limiting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Aircraft windshield wiper systems face challenges in preventing over-rotation of the wiper arm, which can lead to damage to the wiper components and the aircraft's windshield, especially when using reversible brushless direct-current motors that lack effective motion stops.
Innovation Solution
The implementation of a reversible motor with a ball nut mechanism that includes forward and aft stops, along with guide pins, to translate the ball nut along the aft shaft segment, preventing over-rotation by stopping the motor when the ball nut contacts these stops, thereby limiting the wiper arm's sweep angle and preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reversible brushless direct-current motor is used to drive the wiper arm, then the motor can achieve oscillatory motion directly and provide precise control, but the motor lacks effective motion stops which can lead to over-rotation and damage to components
Solution Approach 1:
The patent implements motion stops (forward stop and aft stop) that are pre-positioned within the motor housing to prevent over-rotation before damage can occur. The ball nut mechanism translates the shaft's rotational motion into linear motion that directly engages these stops, providing preliminary protection against excessive sweep angles.
Solution Approach 2:
The ball nut acts as an intermediary mechanism between the motor shaft and the motion stops. It converts the rotational motion of the shaft into linear translational motion, allowing the stops to effectively limit the wiper arm's sweep angle without directly interfering with the motor's rotational control.
2Reliability
If motion stops are implemented to prevent over-rotation, then component damage is prevented, but the system complexity increases due to additional mechanisms
Solution Approach 1:
The patent merges the motion stop mechanism with the motor housing itself. The forward stop and aft stop are integrated into the housing structure, and the ball nut mechanism is contained within the same housing, eliminating the need for separate external stop mechanisms and reducing overall system complexity.
Solution Approach 2:
The ball nut mechanism is nested within the motor housing, with the shaft extending through the housing and the ball nut translating along the shaft within the confined space of the housing. This nested arrangement allows the motion stops to be embedded within the existing motor structure without adding external complexity.
3Reliability
If the ball nut mechanism is used to translate motion and engage stops, then over-rotation is prevented, but friction and wear increase on the motor components
Solution Approach 1:
The patent replaces direct mechanical engagement between the shaft and stops with a ball nut mechanism that uses threaded engagement. This substitution allows for smoother motion translation and reduces sliding friction compared to direct contact between the shaft and stop surfaces.
Solution Approach 2:
The ball nut mechanism changes the nature of the mechanical interaction from direct sliding contact to threaded rolling contact. This parameter change in the contact type reduces friction and wear on the motor components while still effectively limiting the wiper arm's motion through the engagement of the ball nut with the forward and aft stops.
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
This solution effectively prevents over-rotation of the wiper arm, reducing wear on the motor and protecting aircraft components by utilizing a ball screw mechanism with motion stops integrated within the motor housing, ensuring reliable operation and minimizing potential damage from excessive sweep.
Implementation Method 1
a ball nut, wherein the ball nut translates along the aft shaft segment from rotation of the aft shaft segment
Implementation Method 2
the first guide pin extends through the first passage in the flange of the ball nut and prevents rotation of the ball nut relative to the stator when the aft shaft segment rotates
Data Source
AI summary
Disclosed is an aircraft windshield wiper system, having: a wiper arm; a reversible motor that drives the wiper arm, the motor including: a stator; a rotor configured to rotate relative to the stator; a forward shaft segment that is driven by the rotor and being rotationally connected to the wiper arm; an aft shaft segment that is driven by the rotor, the aft shaft segment including a forward end and an aft end; a ball nut that translates along the aft shaft segment from rotation of the aft shaft segment; a forward stop at a forward end of the aft shaft segment, configured to stop forward translational motion of the ball nut along the aft shaft segment; and an aft stop at an aft end of the aft shaft segment, configured to stop aft translational motion of the ball nut along the aft shaft segment.