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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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Potential Applications for water hydraulics
#4
• 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).
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
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
#8
Goal : To carefully design the lubricating interface of water hydraulic external gear machines that
• Supports high pressure loads• Minimizes leakages
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Axial Balance
#9
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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Methodology
#10
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)
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Micro-surface shaping effects
#11
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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Wedged gears – Oil as the working fluid
#12
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)
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
• 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. . .
#13
Iterative procedure
C++, OpenFOAM, GSL, Shell scripting
Optimal Axial Balance Flowchart
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Objective Function 1 – Total power loss from the lateral gaps
#14
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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Results : Wedged gears – with water as the working fluid (preliminary)
#15
• 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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
Conclusion
#16
• 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
Divya Thiagarajan, Andrea VaccaSurface shaping in water hydraulic EGMsFPIRC 2015
THANK YOU
Divya Thiagarajan, Andrea Vacca
Maha Fluid Power Research Center,
Purdue University, West Lafayette, IN, USA
[email protected], (765)-409-9672
#17