Self-Contained Reduction Gear with Automatic Ratio Switching
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Solution Overview
Problem
Existing systems for aircraft engines require separate starters and generators, leading to increased weight, dimension, and cost due to the need for high torque at low rotation speeds for starting and excessive speed when generating, and existing solutions with large reduction ratios fail to efficiently manage these transitions without external control.
Innovation Solution
A self-contained reduction gear with two gears having different tooth reduction ratios and a reversible electrical machine, where the reduction gear automatically switches between two reduction ratios by inverting axial forces on helical teeth, preventing simultaneous gear engagement and allowing operation at suitable speeds in both starter and generator modes without external control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a large reduction ratio is used between the electrical machine and the engine, then the engine can be started at lower torque and higher speed of the machine, but the speed of the machine when functioning as generator becomes excessive
Solution Approach 1:
The reduction gear ratio is made dynamically adjustable through two different gear configurations (first gear ratio and second gear ratio). The system automatically selects the appropriate gear ratio based on operational mode: first gear ratio during starting to reduce speed and increase torque, second gear ratio during generation to accommodate higher speeds, thereby resolving the contradiction between starting torque requirements and generator speed requirements
Solution Approach 2:
The invention changes the transmission ratio parameter from a fixed value to a variable value that can switch between two discrete values. By modifying the gear ratio parameter according to operational conditions (starting vs. generation mode), the system optimizes both torque multiplication during starting and speed compatibility during generation, eliminating the need for a single oversized gear ratio
2Weight of moving object
If a single electrical machine is used for both starting and electricity generation, then weight and system complexity are reduced, but the machine must operate at conflicting speed requirements
Solution Approach 1:
The electrical machine is designed to perform multiple functions (starting and electricity generation) by combining it with a reduction gear that provides two different reduction ratios. The reduction gear acts as an adaptive interface that enables the single electrical machine to operate efficiently in both modes by adjusting the speed-torque relationship, thereby achieving universality without compromising performance
Solution Approach 2:
The reduction gear provides dynamic adaptability through automatic switching between two gear ratios based on the operational state. During starting, the first gear ratio matches the electrical machine's high-speed low-torque output to the engine's low-speed high-torque requirement. During generation, the second gear ratio accommodates the electrical machine's operating speed at engine cruising speeds, enabling a single machine to handle conflicting speed requirements
3Device complexity
If automatic switching between reduction ratios is implemented without external control, then system complexity is reduced, but reliability of preventing simultaneous gear engagement must be ensured
Solution Approach 1:
The reduction gear system is designed to automatically switch between gear ratios using the inherent axial forces generated during operation. The axial forces on the helical teeth naturally push the mobile toothed wheel toward engagement with one gear or the other based on the direction of rotation and loading conditions, eliminating the need for external control mechanisms while maintaining reliable automatic switching between starting and generation modes
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 solution enables reliable automatic mode switching of the electrical machine between starter and generator without external control, ensuring efficient operation at appropriate speeds and preventing accidental gear engagements, thus reducing system weight, complexity, and cost.
Implementation Method 1
the teeth of the mobile toothed wheels are helical and have inclinations in the same tangential direction relative to the first shaft
Implementation Method 2
The changeover of the electrical machine from starter mode to generator mode, or vice versa, is accompanied in the reduction gear by an inversion of axial forces on the helical teeth, that are responsible for translation movements of mobile toothed wheels
Implementation Method 3
the first shaft carries a freely sliding spacer, that can come into contact with the two mobile toothed wheels simultaneously, keeping them at an distance that prevents the gear positions from being engaged simultaneously
Data Source
AI summary
The reduction gear includes a pair of gears installed in parallel between two shafts and each provided with a mobile wheel free to move axially to engage in turn with one of the shafts and to transmit movement with different ratios. Since the gear teeth are helical, opposite forces on the reduction gear make it changeover from one reduction ratio to the other. No external control is necessary. Application to mechanical transmissions between an engine and a reversible electrical machine (starter or generator), that starts the motor with a large speed reduction and generates electricity with a smaller reduction.