Investigation of micro surface shaping effects for...

Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015

Investigation of micro surface shaping effects for improving the lubrication performance of water

based high pressure external gear machines

Divya Thiagarajan (presenter) Prof. Andrea Vacca

Maha Fluid Power Research CenterSchool of Mechanical Engineering

Purdue University, USA14th October 2015


Outline

#2

• Introduction to water hydraulics

• Designing water based EGMs and concerns

• Simulation models used

• Micro-surface shaping effects– Linear wedge gears– Step + wedge gears– Results

– Conclusion


Introduction

#3

Why is water an attractive alternative hydraulic fluid to oil?

• Non-flammable, environment friendly, non-toxic• Negligible contamination problems• Easy availability and relatively low cost• Lower friction losses due to lower viscosity• Superior cooling capacity• High bulk modulus

• Leakage issues • Cost of disposal• Environmental hazards• Safety• Availability

Fluctuating oil prices

Potentials of waterCurrent issues with oil


Potential Applications for water hydraulics

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• Mining• Offshore• Food processing• Metal Production• Desalination• Waterways• Agriculture• Potential medical

applications• ....Many more possible

Source : Krutz, G. W., & Chua, P. S. (2004, February). Water hydraulics—theory and applications 2004. In Workshop on Water Hydraulics, Agricultural Equipment Technology Conference (AETC’04) (pp. 8-10).


Water hydraulics - Major Challenges

#5

• Low viscosity creates poor lubrication characteristics and poor sealing abilities• Can cause problems of corrosion• Risk of cavitation due to high vapor saturation pressures – can cause erosion problems• Low viscosity of the fluid makes surface finishes and surface conformity critical• Risk of freezing• Microbial growth

High pressure water hydraulics – key for promoting the technology

Lubrication and sealing characteristics of the working fluid are the biggest challenges in high pressure positive displacement machines

Most critical design component - Positive displacement machines

Problems can be solved by


State of the art

#6

• Danfoss PAH/MAH series pumps/motors – Nessie Series• The Water Hydraulics Co. Ltd• Wittkop, W., & Samland, U. (1992). ”High-pressure water pump having a

polyetheretherketone cylinder bushing for pure water.” U.S. Patent No. 5,131,818.Washington, DC: U.S. Patent and Trademark Office. (Claim : Pressures upto 450 bar)

• Many low pressure low cost water hydraulic external gear pumps

Water hydraulic pumps/motors

• Existing water hydraulic pumps/motors are limited to a maximum operating pressure of 160 bar

• No water hydraulic external gear machine operating at pressures > 50 bar currently exists in the market


inlet

outletLateral gaps

Radial gaps

Lateral lubricating interface in external gear machines is the first critical component to address while designing high pressure external gear machines

using water

Main source of power losses

- Mechanical Losses (Viscous friction)

- Volumetric Losses (Leakage flows)

Main functions of the lateral gap

+ Sealing

+Bearing loads

High tolerance to contamination

Well suited for open center solutions

Relatively compact and low cost design

Lower cavitation problems

Lesser noise pulsations

External Gear Machines

#7


lateral bushes (pressure plates) casing

gears

lateral lubricating

gapFout

Fin

Lubricating interface design• Low leakages– low gap heights• No wear, Low shear losses– gap

high enough to prevent boundary lubrication and wear

axially balanced bushes

Designing water based EGMs

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Goal : To carefully design the lubricating interface of water hydraulic external gear machines that

• Supports high pressure loads• Minimizes leakages


Axial Balance

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Forces Representation Direction

Towards gears

Away from gears

Fbalance

FTSV + Gap

High Pressure Balance AreaSeal

Low Pressure Balance Area

Determining balancing areas can design the axial balance of

EGMs!

Is hydrostatic balancing sufficient?

Hydrodynamic effects are necessary


Methodology

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Advanced numerical tools can be carried out in the investigation of micro surface shaping effects

• HYGESim tool for simulating external gear machines• TEHD model for the lateral lubricating interfaces of external gear machines

Dhar, Vacca (2014)Vacca, Guidetti (2011)


Micro-surface shaping effects

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Shot peened gears Waved gears

- Dhar (2014)

Wedged gears

Shot peened lateral bushing

• Shot peening does not appear to improve the lubrication performance

• Waved gears can be difficult to manufacture

• Wedged gears is the potential option – can be implemented with water

Lubricant film thickness scaled upto ~10000 times for visibility


Wedged gears – Oil as the working fluid

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Idea :• Linear sloping wedge on either

surface of the gear teeth• To have positive load carrying

capacity, lubricant film thickness must decrease in the sliding direction.

• Dhar (2014)

FSI-EHD model results with wedged gears with maximum wedge depth = 1 µm

Maximum improvement in power loss ~ 66 %

Axial balance needs to be optimal when changes with surface shaping as well as working fluid is

changed

An automatic numerical procedure for optimizing the axial balanceof external gear machines has been developed.

- Thiagarajan, Vacca (2014)


• Delivery pressure• Shaft speed• Fluid temperature

Operating Condition 1

Operating Condition 2

Initialize grid of design parameters

Run simulations using design grid

FSI-EHD model for lateral lubricating gaps

Evaluate objective functionsI. Power LossesII. Gap Non Uniformity Index

Find “best feasible” solution in the current grid

Convergence criterion reached?

Define modified new grid

Optimized balance area design obtained

Yes

No

Operating Condition N. . .

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Iterative procedure

C++, OpenFOAM, GSL, Shell scripting

Optimal Axial Balance Flowchart


Objective Function 1 – Total power loss from the lateral gaps

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Velocity field in the gap/Leakage

This is then integrated over the boundaries to find leakage losses

𝜏𝑧𝑥 = −ℎ

2

𝜕𝑝

𝜕𝑥−𝜇𝑢𝑔

ℎ

𝜏𝑧𝑦 = −ℎ

2

𝜕𝑝

𝜕𝑦−𝜇𝑣𝑔

ℎ

Viscous Friction/ Shear losses

𝑃𝑙𝑜𝑠𝑠 = 𝑄𝑙𝑒𝑎𝑘∆𝑃

𝑃𝑙𝑜𝑠𝑠 = 𝐓.𝛚

𝐓 =

𝑖

2𝐴𝑖(𝐫𝐢 × 𝛕𝐢)

Axially balanced bushing design• Low leakages– low gap heights –

low losses due to leakages• No wear, Low shear losses– gap

high enough to prevent boundary lubrication and wear

Optimal balance between the two opposing sources of power losses is desired


Results : Wedged gears – with water as the working fluid (preliminary)

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• 200 bar 2000 rpm

• 13.31 % decrease in total losses (volumetric + mechanical) with respect to original balance with wedged gears

• 80 bar 1000 rpm

Gap film thickness results


Conclusion

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• Initial steps towards designing a water hydraulic external gear machine waspresented with a focus on the lubrication performance

• Wedged gears were shown to improve the lubrication performance of waterhydraulic external gear pumps

• Future work involves prototyping and testing the EGM for water as the workingfluid


THANK YOU

Divya Thiagarajan, Andrea Vacca

Maha Fluid Power Research Center,

Purdue University, West Lafayette, IN, USA

[email protected], (765)-409-9672

#17

mailto:[email protected]

Investigation of micro surface shaping effects for...

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