Bi-metal Pump Gear Segmentation for Wear and Machinability
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Solution Overview
Problem
Existing pump gears face challenges in achieving wear resistance while maintaining machinability of drive splines and threaded features, particularly in high-temperature, low-lubricity environments like aircraft engines, where wear increases maintenance costs and operational life is impacted.
Innovation Solution
A bi-metal shaft arrangement is used, where the first shaft is made from low vanadium tool steel for machinable drive splines and the second shaft from high vanadium tool steel for improved wear resistance, brazed together to form a pump gear with integral gear portions and splines, allowing for conventional machining and enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high vanadium tool steel material is used for the pump gear shaft, then wear resistance of the spur gear is improved, but machinability of the drive spline deteriorates
Solution Approach 1:
The pump gear shaft is divided into two separate shafts: a first shaft made from high vanadium tool steel (greater than 9% vanadium) for the spur gear portion, and a second shaft made from low vanadium tool steel (less than or equal to 1% vanadium) for the drive spline portion. This segmentation allows each shaft to be optimized for its specific function - the first shaft provides superior wear resistance for gear teeth, while the second shaft enables easy machining of drive splines using conventional practices.
Solution Approach 2:
Different regions of the pump gear shaft are made from different materials with locally optimized properties. The first shaft portion (gear section) uses high vanadium content material specifically where wear resistance is critical for gear tooth engagement, while the second shaft portion (drive spline section) uses low vanadium content material where machinability is the priority for creating precise spline features.
2Reliability
If wear resistant material is used for the pump gear, then gear tooth wear is reduced, but the size and weight of the pump gear increase
Solution Approach 1:
The pump gear is segmented into two shafts of different materials and weights. The first shaft with high vanadium content provides the necessary wear resistance for gear operation, while the second shaft with low vanadium content is lighter and easier to machine. The combined weight of the bi-metal construction is less than what would be required if the entire shaft were made from the heavier, more wear-resistant high vanadium material.
3Ease of manufacture
If the pump gear is made from a single unitary material, then manufacturing cost is reduced, but wear resistance and machinability cannot be simultaneously optimized
Solution Approach 1:
Rather than using a single material compromise, the invention segments the pump gear into two separately manufactured shafts that are subsequently joined. This allows each shaft to be made from the optimal material for its specific function, and the joining process (brazing, welding, or mechanical connection) is more cost-effective than the alternative of using expensive high vanadium material for the entire shaft or using complex machining processes on difficult-to-machine materials.
4Adaptability or versatility
If a longer pump gear shaft is used to provide additional functions, then mounting provisions for auxiliary components are achieved, but machining difficulty and cost increase
Solution Approach 1:
The longer shaft needed for auxiliary mounting provisions is implemented only in the second shaft (low vanadium material), which is dedicated to drive spline and threading features. This segmentation allows the extended portion to be easily machined with conventional practices, while the first shaft (high vanadium material) maintains its focus on gear tooth strength and wear resistance without the added machining complexity.
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 bi-metal shaft arrangement reduces gear tooth wear in high-temperature jet fuel applications, maintaining machinability and reducing material costs while improving operational life and reliability, fitting within existing space and weight constraints.
Implementation Method 1
A second shaft is arranged having a third end brazed to the first end
Data Source
AI summary
A pump gear is provided. The pump gear includes a first shaft portion having a first end and a second end with an integral gear portion formed therebetween. The first shaft portion is made from a first tool steel material. A second shaft portion having a third end brazed to the first end. The second shaft portion has at least one integral drive spline formed adjacent one end. The second shaft portion is made from a second tool material. The first tool steel material has a vanadium content by weight of greater than 9% and the second tool steel material has a vanadium content by weight of less than or equal to 1%.