Wiper Drive Shaft Hard Stops for Over-Sweep Protection
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Solution Overview
Problem
Current windshield wiper systems lack a safety feature to prevent the wiper arm assembly from oversweeping beyond a fixed sweep angle, which can cause damage to the airframe or fracture of external wiper system components.
Innovation Solution
A wiper drive shaft with external threads and mechanical hard stop grooves, including first and second hard stop positions defined by circlips, to restrict the axial movement of a nut along the shaft, preventing over-sweep by triggering an overcurrent condition in the motor when the nut reaches the hard stop positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a reversible motor system is used to enable the wiper arm to sweep through a fixed angle, then the wiper system can operate bidirectionally to clean the windshield, but the system lacks a safety feature to prevent over-sweep beyond the fixed sweep angle which can cause damage to the airframe or fracture of external wiper system components
Solution Approach 1:
The patent applies preliminary action by pre-positioning mechanical hard stops (circlips) on the wiper drive shaft at predetermined axial locations that correspond to the maximum sweep angles. These hard stops are installed before operation and automatically engage with the nut to prevent over-sweep, eliminating the need for complex software-based protection and providing inherent mechanical safety against airframe damage and component fracture.
Solution Approach 2:
The patent replaces potential software-based or sensor-based over-sweep detection systems with a purely mechanical hard stop mechanism. The circlips mounted on the threaded drive shaft create physical barriers that directly engage with the nut, converting the control function from electronic to mechanical, thereby providing reliable, fail-safe over-sweep protection that cannot be bypassed by software errors or sensor failures.
2Ease of operation
If the wiper drive shaft is allowed to rotate freely to achieve the desired sweep angle, then the wiper arm can reach its full operational range, but the system cannot prevent rotation beyond the start position or end sweep position which causes damage
Solution Approach 1:
The hard stops (circlips) are pre-installed on the wiper drive shaft at axial positions that precisely correspond to the desired start and end sweep positions. This preliminary positioning ensures that the full operational sweep range is available while automatically preventing any rotation that would cause the wiper arm to contact the airframe or damage external components.
Solution Approach 2:
The nut acts as an intermediary element between the rotating drive shaft and the stationary circlips. As the drive shaft rotates, the nut travels axially along the threaded shaft and is mechanically blocked by the circlips at the hard stop positions. This intermediary mechanism allows full sweep range motion while mediating to prevent harmful over-rotation that would damage the airframe.
3Reliability
If a mechanical hard stop system is added to prevent over-sweep, then safety is improved, but the device complexity increases with additional components such as hard stop grooves, circlips, and axial positioning features
Solution Approach 1:
The patent merges the hard stop function with the existing threaded drive shaft by machining grooves directly into the shaft and mounting circlips on these grooves. This integration combines the motion transmission function of the threaded shaft with the over-sweep protection function of the hard stops, eliminating the need for separate protection mechanisms and reducing overall system complexity while maintaining reliable over-sweep prevention.
Solution Approach 2:
The wiper drive shaft is designed with multi-functionality by incorporating both the motion transmission capability (through external threading) and the over-sweep protection capability (through integrated hard stop grooves and circlip mounting features) into a single component. This universal design allows the drive shaft to simultaneously perform driving and safety functions, reducing the number of separate parts and simplifying the overall mechanism.
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 effectively prevents over-sweep of the wiper arm by mechanically limiting the rotation of the wiper drive shaft and shutting down the motor when an overcurrent condition is detected, thereby protecting the airframe and wiper system components.
Implementation Method 1
A wiper drive shaft configured to drive a wiper arm between a start position and an end sweep position. The wiper drive shaft includes external threads defined therein and at a distal end thereof. An axial length of the external threads along the wiper drive shaft defines the start position and the end sweep position
Implementation Method 2
A first circlip can be disposed in the first hard stop groove and a second circlip can be disposed in the second hard stop groove. The first and second circlips can be configured to prevent axial movement of the nut along the wiper drive shaft beyond the first and second circlips to prevent the wiper drive shaft from rotating beyond the start position and the end sweep position
Implementation Method 3
A controller can be operatively connected to the motor configured to control the motor and the controller can include an overcurrent module configured to sense an overcurrent condition in the motor and to shut down the motor when an overcurrent condition is detected
Data Source
Figure 1
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Figure 3A
AI summary
In accordance with at least one aspect of this disclosure, a system (100) includes a wiper drive shaft (116) configured to drive a wiper arm (106) between a start position (110) and an end sweep position (112). The wiper drive shaft (116) includes external threads (132) defined therein and at a distal end (134) thereof. An axial length of the external threads (132) along the wiper drive shaft (116) defines the start position (110) and the end sweep position (112), and a total desired sweep angle between the start position (110) and end sweep position (112). The wiper drive shaft (116) includes a first hard stop groove (136) and a second hard stop groove (138), each defined at a respective first axial offset and a second axial offset from the external threads (132) to define a first hard stop position (140) and second hard stop position (142).