Compact Gearbox with Reduced Backlash for Aircraft Actuators
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Solution Overview
Problem
Existing flight control actuators for aircraft require significant space due to the use of linear actuators, which limits their integration in aircraft components like the tailplane or wing, as they need to accommodate the actuator at full extension, leading to space constraints.
Innovation Solution
A gearbox design incorporating two axially spaced epicyclic gear trains with helical planet and output gears, where the planet carriers are mounted on an axial shaft with limited axial motion and urged into engagement using springs or Belleville washers, ensuring equal torque transmission and minimizing backlash through load catching shafts and opposite handed helical engagements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a linear actuator is used to achieve very low backlash, then the actuator can accommodate full extension, but this requires a considerable amount of space inside the tailplane or wing
Solution Approach 1:
The patent replaces the linear actuator mechanical system with a rotary actuator combined with a gearbox. The gearbox converts rotary motion to linear motion at the output, allowing the actuator body to remain compact while still achieving the required stroke length, thereby reducing the space needed inside the tailplane or wing while maintaining low backlash through precision gear engagement
Solution Approach 2:
The patent employs a nested structure where the planet gears are positioned within the annulus, and the sun gear is centrally located. This nested arrangement allows all gear components to be compactly integrated within a small volume, enabling the rotary actuator to achieve the required output stroke without requiring the extensive space needed by a linear actuator
2Volume of moving object
If a gearbox with two epicyclic gear trains is used to reduce space, then the actuator becomes compact, but the complexity of the gear train increases
Solution Approach 1:
The patent merges two epicyclic gear trains into a single integrated gearbox unit sharing common components (input shaft, housing, lubrication system). This consolidation achieves the required compact size and torque multiplication while managing complexity through shared infrastructure and standardized component interfaces
Solution Approach 2:
The planet gears serve multiple functions: they transmit torque from the sun gear to the annulus, provide mechanical advantage for torque multiplication, and their helical configuration simultaneously reduces backlash and distributes load across multiple contact points, simplifying the overall design
3Power
If helical gears with opposite handedness are used to minimize backlash, then torque transmission is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent utilizes the helical angle and handedness as key parameters to achieve backlash elimination. By carefully selecting complementary helical angles for the planet gears and annulus, the design transforms the engagement characteristics to provide inherent backlash compensation while maintaining manufacturability through standard helical gear cutting processes
Solution Approach 2:
The helical tooth profiles act as intermediaries that gradually engage and disengage gear teeth, distributing the contact load over a longer path and reducing shock loads. This intermediary engagement mechanism facilitates smoother torque transmission and reduces the sensitivity to minor manufacturing variations
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 design allows for a compact rotary flight control actuator with reduced backlash, enabling efficient torque transmission and overcoming space constraints, making it suitable for aircraft components with limited space.
Implementation Method 1
The planet carriers may be urged by springs or by Belleville washers
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a gearbox with reduced backlash. The gearbox (100, 150) includes two axially spaced epicyclic gear trains, each having a sun gear (18), axially spaced planet gears carried by a planet carrier (16), and a ring gear fixed to the gear box. One of the planet gears engages with the fixed ring gear, and another of the planet gears (120) engages with an output ring gear (122). The sun gears (18) of the two gear trains are mounted on a single shaft (20). The planet carriers (16) of the two gear trains are mounted on a shaft (110) so that they can freely rotate but have limited axial motion along the shaft (110). The two output ring gears (122) are helical gears of opposite handedness.