Logan T Williams 572020 Naval Research Laboratory Washington DC 20375 Gear pumps are a ubiquitous means to generate hydraulic power Rugged simplicity cost effective The simplicity of gear pump design presents some liabilities ID: 929106
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Slide1
Curvilinear Circular-Arc Tooth Gears for Use in Gear Pumps
Logan T. Williams
5/7/2020
Naval Research Laboratory, Washington D.C., 20375
Slide2Gear pumps are a ubiquitous means to generate hydraulic powerRugged simplicity, cost effective
The simplicity of gear pump design presents some liabilities
Lower volumetric efficiencyNoise generationGear wearWhile gear pump architecture has a long tradition, there is there still room for improvementA novel gear configuration that improves pump performance without requiring costly pump redesigns
Overview
Slide3Pump operating principle is the meshing of two gears
Un-meshing teeth provide suction
Meshing teeth generate fluid pressureWear plates added for high-pressure operationProvides tighter seal along axial gear face and reduces leakageReview of Gear Pumps
Slide4Most common gear used is the involute spur gear
Constant line of action
Easy to manufactureLong heritageInvolute Gears
Volume between teeth not fully swept during mesh
Creates trapped pocket of fluid
Slide5Meshing action pressurizes fluid pocket
Fluid compressed faster than it can escape
Creates large pressure oscillations within the pocketCreates noise Causes gear tooth damageCommon response is to add a relief groove to the wear plateProvides larger exit area for trapped fluidReduces pressure oscillation magnitude
Treats the symptom, but not the cause
Gear Mesh Dynamics
Tip damage
Slide6Helical gears for gradual mesh
Reduces noise and tooth stress
Eases fluid expulsion from tooth spaceNon-involute tooth profileEach tooth space fully swept by mating gear toothEliminates trapped fluid pocketCommercial State of the Art
Helical gears in Rexroth Silence Plus
1
Helical non-involute gears
2
1
Bosch Rexroth, Silence Plus promotional video, https://www.youtube.com/watch?v=bgXlozmCwmQ
,
published 5/14/2011
2
Mitome
, K. and Seki, K., “A New Continuous Contact Low-Noise Gear Pump,”
Journal of Mechanisms, Transmissions, and Automation in Design
,
105
, No. 4, 1983, pp. 736-741.
Slide7Helical gears induce axial loads during mesh
Requires thrust bearings or pressure compensation channels in wear plates
Non-involute gears require precise shaft placementSensitive to assembly tolerances and vibrationWhat can be done to address the underlying issues with involute spur gears while maintaining their advantages?Current Design Challenges
Slide8First goal:
Attain benefits of gradual mesh
Minimize net axial loadGradual mesh inherently induces axial loadRequires a symmetric axial profile to balance forcesHerringbone gear is one such example, but difficult to fabricateCurvilinear profiles offer similar advantagesGradual mesh, zero net load
Much easier to manufacture
Symmetric Axial Profile
Slide9Second goal is to create a tooth profile that fully sweeps itself
Eliminates trapped fluid pocket
Flexible profile consisting of multiple curvesTooth tip curve conforms to root curveCan be tailored to specific applicationsCurves are spliced to provide smooth transitionNominal configuration:Circular arc for tip and root
Fully sweeps out mating tooth
Involute curve for flank
Provides tolerance to lateral misalignment
Hybrid Tooth Profile
Slide10Combine the two desired gear elements:
Curvilinear axial profile
Circular-involute hybrid tooth profileCurvilinear gears offer gradual meshing with no axial loadingRemoves the need for compensation mechanismsEnables drop-in replacement of spur gearsHybrid tooth profile fully sweeps tooth space while preserving involute tooth flankNo trapped fluid pockets
Greater tolerance of parallel misalignment
Novel Solution: CCAT Gears
Slide11Compared CCAT gears with equally-sized involute spur gears
Tested in custom NRL gear pump (1.5 x 1.6 x 1.8 in.)
Gear OD 0.6875 in.Volumetric efficiency improved approx. 10%Sound level reduced approx. 7 dBPreliminary Performance
Slide12The CCAT gear offers a drop-in replacement of spur gears that:Reduces operating noise
Increases volumetric efficiency
While designed with gear pumps in mind, can be leveraged for other applicationsGear boxes, shaft power transmissions, etc.Current status:Patent application receivedMore detailed discussions regarding applications and transition can be made under a NDA
Conclusions