Variable Block Shaft Geometry for Constant-Frequency IDG Speed Trimming
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Solution Overview
Problem
Integrated drive generators in aircraft face challenges in maintaining a constant frequency of electric power generation due to varying input shaft speeds from gas turbine engines, which is not effectively addressed by existing speed trimming hydraulic units with variable block shafts.
Innovation Solution
A replacement method for the variable block shaft in the hydraulic unit involves a new shaft design with specific dimensions and spline connections, along with a swash plate arrangement to control the speed and direction of hydraulic fluid flow, ensuring a constant speed is transmitted to the generator, thereby stabilizing the frequency of generated electric power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a variable block shaft is used in the hydraulic unit to trim speed, then the speed control capability is improved, but the manufacturing precision and reliability deteriorate due to the complex geometry and bearing race surface requirements
Solution Approach 1:
The patent applies parameter changes by modifying the ratio relationship between two critical dimensions: the outer diameter of the inner bearing race surface and the axial length of the inner bearing race surface. By establishing a specific ratio range (3.70-3.95) between these parameters, the invention optimizes the speed control capability while maintaining manufacturability and reliability, resolving the contradiction between performance and manufacturing precision.
2Speed
If a variable block shaft with complex geometry is used to achieve speed trimming, then the speed control capability is improved, but the device complexity increases
Solution Approach 1:
The patent resolves the complexity issue by establishing a specific ratio relationship between the outer diameter and axial length of the inner bearing race surface. This parameter-based approach provides a systematic design criterion that simplifies the overall device complexity while maintaining the necessary speed control capability through controlled geometric relationships.
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 new shaft design effectively stabilizes the speed and direction of rotation within the hydraulic unit, ensuring a constant desired frequency of electric power generation by precisely controlling the speed trimming process, addressing the variability in input shaft speeds.
Implementation Method 1
a swash plate arrangement to control the speed and direction of hydraulic fluid flow
Implementation Method 2
The cylinder block has a spline connection to a variable block shaft
Data Source
Figure 1
Figure 2~3
Figure 4A~4C
AI summary
A variable block shaft has a radially enlarged disc (198) formed at a first end (193). A shaft portion extends from the disc to a second end. An inner bearing race (204) surface is defined intermediate the first and second end and has an outer peripheral surface. An axial length of the inner bearing race surface is defined between inner facing surfaces of lands at each axial side. The axial distance is measured along the center axis of the body and an outer diameter to the inner bearing race surface being defined as a first distance. The axial length of the inner bearing race surface is defined as a second distance and a ratio of the first distance to the second distance being between 3.75 and 3.90. An integrated drive generator and a method are also disclosed.