Aircraft Fuel Pump Shared Journal Shaft Stability
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Solution Overview
Problem
Multi-stage gear pumps in aircraft gas turbine engines face instability and premature wear due to varying operational demands, leading to tooth bounce and bearing oil whirl, particularly when switching between single and multistage modes, which increases weight, size, and energy consumption.
Innovation Solution
A multi-stage pump assembly with a shared journal shaft and pressurized bearing arrangement, where a spacer is fixed between the first and second gear pumps, ensuring continuous loading of journals and reducing tooth load, thereby minimizing instability and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the first gear pump is operated at reduced pressure state to reduce energy consumption during cruise and idle operations, then energy consumption is reduced, but tooth bounce and instability occur leading to gear tooth failure
Solution Approach 1:
A shared journal shaft is introduced as an intermediary element that connects both the first and second gear pumps. This shared shaft acts as a mediator that distributes and balances the loading between the two gear stages, preventing tooth bounce and instability in the first pump even when operating at reduced pressure during cruise and idle conditions.
Solution Approach 2:
The first and second gear pumps are merged onto a single shared journal shaft instead of operating independently. This combining allows the two gear stages to share the rotational load and work together as an integrated system, eliminating the instability issues that occur when the first pump operates alone at reduced pressure.
2Use of energy by moving object
If the first gear pump is operated at reduced pressure state, then energy consumption is reduced, but bearing oil whirl occurs leading to bearing failure
Solution Approach 1:
The shared journal shaft serves as a stabilizing intermediary that maintains proper bearing loading. By connecting both gear pumps to the same shaft, the system ensures that the bearings supporting the shaft remain adequately loaded even when the first pump operates at reduced pressure, preventing bearing oil whirl and extending bearing life.
3Reliability
If conventional arrangement drives the second gear stage through the tooth mesh of the first gear stage, then tooth instability and bearing oil whirl are alleviated, but gear teeth size or count must increase increasing weight
Solution Approach 1:
Both gear stages are merged onto a single shared journal shaft, allowing them to operate as an integrated unit. This eliminates the need for one gear stage to drive the other through tooth mesh, as both stages are directly driven by the shared shaft. Consequently, the gear teeth can be smaller and lighter while maintaining stability, reducing the overall weight of the pump assembly.
4Reliability
If offset arrangement of first and second gear pumps is used, then independence issues are addressed, but additional components, wear, weight, and size are added
Solution Approach 1:
The first and second gear pumps are merged onto a single shared journal shaft in a compact arrangement. This eliminates the need for separate independent drive mechanisms and offset positioning, reducing the number of components, minimizing wear surfaces, and decreasing both the weight and overall size of the pump assembly while maintaining operational stability.
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 stabilizes the gear and bearing system, reduces tooth bounce, and minimizes energy consumption by maintaining journal loading, even during reduced pressure operations, extending the life of the pump and reducing overall weight and size.
Implementation Method 1
A multi-stage pump assembly includes a housing receiving a first gear pump. The first gear pump has a first drive journal shaft that rotates about a first axis and drives a first gear
Implementation Method 2
The first gear pump has a first drive journal shaft that rotates about a first axis and drives a first gear that operatively engages a second gear rotating about an adjacent second axis
Implementation Method 3
A spacer is interposed between the first and second gear pumps and fixed to the housing
Data Source
AI summary
A multistage gear pump assembly includes first and second gear pumps that use common shafts and are axially separated by a fixed spacer within the housing. Pressurized bearings are provided at opposite axial ends of the first and second gear pumps. The second gear pump handles cruise and idle operations of the aircraft while the first gear pump stage assists in meeting higher demand modes of engine operation. Otherwise, the first gear pump is maintained at a minimal pressure to reduce energy consumption and still provide desired stability and eliminate issues associated with bearing oil whirl associated with prior known arrangements. When additional assistance is required, such as during takeoff, climb, or windmill relight, the first gear pump advantageously contributes to the increased pressure.